UI/UX: Use better icons for player-related things

- Add and use new icons
- Make some labels more explicit
- Properly document copyright of both the new icons, and the icons used to make them
  - Note that the Cartoon icons fall under the same copyright as all other Cartoon icons, so no licenses.txt update is needed

data/gui/dialogs/online/user_info_dialog.stkgui

@@ -22,15 +22,15 @@
             <icon-button id="cancel" width="64" height="64" icon="gui/icons/back.png"
                          I18N="User info dialog" text="Close" label_location="bottom"/>
             <icon-button id="remove" width="64" height="64" icon="gui/icons/remove.png"
-                         I18N="User info dialog"  text="Remove" label_location="bottom"/>
-            <icon-button id="friend" width="64" height="64" icon="gui/icons/blue_plus.png"
+                         I18N="User info dialog"  text="Remove Friend" label_location="bottom"/>
+            <icon-button id="friend" width="64" height="64" icon="gui/icons/player_add.png"
                          I18N="User info dialog"  text="Add Friend" label_location="bottom"/>
             <icon-button id="accept" width="64" height="64" icon="gui/icons/green_check.png"
-                         I18N="User info dialog"  text="Accept" label_location="bottom"/>
+                         I18N="User info dialog"  text="Accept Invite" label_location="bottom"/>
             <icon-button id="decline" width="64" height="64" icon="gui/icons/red_x.png"
-                         I18N="User info dialog"  text="Decline" label_location="bottom"/>
-            <icon-button id="enter" width="64" height="64" icon="gui/icons/difficulty_medium.png"
-                         I18N="User info dialog"  text="View" label_location="bottom"/>
+                         I18N="User info dialog"  text="Decline Invite" label_location="bottom"/>
+            <icon-button id="enter" width="64" height="64" icon="gui/icons/player_view.png"
+                         I18N="User info dialog"  text="View Profile" label_location="bottom"/>
         </buttonbar>
         <spacer height="1f" width="20"/>
     </div>

data/gui/icons/licenses.txt

@@ -10,16 +10,36 @@ Copyright: SuperTuxKart dev team
 License: CC-BY-SA 3.0
 Comment: Material data
 
-Files: *.png
+Files:
+ *.png
+ back.png
+ player.png
 Copyright: SuperTuxKart dev team
 License: CC-BY-SA 3.0+
 Comment:
  All icons come from Open Game Art (art by onyum.com, comissionned by Bart Kelsey)
- released under CC-BY-SA 3+, options_players & random_kart were tweaked by Marianne Gagnon
+ Released under CC-BY-SA 3+, options_players & random_kart were tweaked by Marianne Gagnon
+ Added in commit: https://sourceforge.net/p/supertuxkart/code/4217/
+
+Files:
+ blue_plus.png
+ down.png
+ player_add.png
+ remove.png
+Copyright: SuperTuxKart dev team, Marc Coll
+License: CC-BY-SA 3.0
+Comment:
+ blue_plus.png, down.png, and remove.png were remixed from back.png, and thus inherit its license.  They were added in https://github.com/supertuxkart/stk-code/commit/2f2547420deb628d8308ef12464b1725ee4160f6
+ player_add.png is a simple combination of player.png and blue_plus.png
+
+Files:
+ player_view.png
+Copyright: SuperTuxKart dev team, Tango Desktop Project
+License: CC-BY-SA 3.0
+Comment: combination of player.png and search.png
 
 Files:
  addons.png
- back.png
  main_*.png
  package*.png
 Copyright: yeKcim (Anthony Carré)
@@ -124,6 +144,10 @@ Comment: From the Gnome icon set. Source: https://github.com/GNOME/adwaita-icon-
 
 Files:
  red_x.png
+ search.png
 Copyright: Tango Desktop Project
 License: CC0
-Comment: An error X symbol icon as emblem. A combination of two icons of project Tango. Source: https://commons.wikimedia.org/wiki/File:Dialog-error-round.svg
+Comment:
+ An error X symbol icon as emblem. A combination of two icons of project Tango. Source: https://commons.wikimedia.org/wiki/File:Dialog-error-round.svg
+ A magnifying glass icon. Source: https://commons.wikimedia.org/wiki/File:System-search.svg
+

data/gui/screens/online/profile_achievements_tab.stkgui

@@ -11,7 +11,7 @@
         <tabs id="profile_tabs" height="2f" x="2%" width="98%" align="center">
             <icon-button id="tab_achievements" width="128" height="128" icon="gui/icons/gp_copy.png"
                 I18N="Section in the profile screen" text="Achievements"/>
-            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/options_players.png"/>
+            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/player.png"/>
             <icon-button id="tab_settings" width="128" height="128" icon="gui/icons/main_options.png"/>
         </tabs>
 

data/gui/screens/online/profile_friends.stkgui

@@ -10,7 +10,7 @@
 
         <tabs id="profile_tabs" height="2f" x="2%" width="98%" align="center">
             <icon-button id="tab_achievements" width="128" height="128" icon="gui/icons/gp_copy.png"/>
-            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/options_players.png"
+            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/player.png"
                 I18N="Section in the profile screen" text="Friends"/>
             <icon-button id="tab_settings" width="128" height="128" icon="gui/icons/main_options.png"/>
         </tabs>

data/gui/screens/online/profile_settings.stkgui

@@ -10,7 +10,7 @@
 
         <tabs id="profile_tabs" height="2f" x="2%" width="98%" align="center">
             <icon-button id="tab_achievements" width="128" height="128" icon="gui/icons/gp_copy.png"/>
-            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/options_players.png" />
+            <icon-button id="tab_friends" width="128" height="128" icon="gui/icons/player.png" />
             <icon-button id="tab_settings" width="128" height="128" icon="gui/icons/main_options.png"
                 I18N="Section in the profile screen" text="Account Settings"/>
         </tabs>

data/gui/screens/online/register.stkgui

@@ -10,7 +10,7 @@
                      I18N="Section in the register screen" text="New Online Account"/>
         <icon-button id="tab_existing_online" width="128" height="128" icon="gui/icons/main_network.png"
                      I18N="Section in the register screen" text="Existing Online Account"/>
-        <icon-button id="tab_offline" width="128" height="128" icon="gui/icons/options_players.png"
+        <icon-button id="tab_offline" width="128" height="128" icon="gui/icons/player_add.png"
                      I18N="Section in the register screen" text="Offline Account"/>
       </tabs>