License documentation work (#4556)

* Properly document licenses of files in icons/android folder

* Fix documentation of two files in Cartoon skin

data/gui/icons/android/license.txt

@@ -1,12 +0,0 @@
-# Licensing work
-
-Icons firstly made for SuperTuxKart UI on Android.
-
-Files: blur_bg_button ; blur_bg_button_focus ; steering_wheel ; drift ; nitro ; nitro_empty ; pause ; thunderbird_reset ; wing_mirror
-	- CC BY-SA 4.0 / author: Néd J. Édoire
-
-# License information:
-
-- Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
-	Visit the following link for detailed informations:
-	https://creativecommons.org/licenses/by-sa/4.0/

data/gui/icons/android/licenses.txt

@@ -0,0 +1,31 @@
+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Upstream-Name: SuperTuxKart
+Upstream-Contact:
+ Marianne Gagnon <auria.mg@gmail.com>
+ Jean-Manuel Clémençon <sam.un@protonmail.com>
+Source: https://supertuxkart.net
+
+Files:
+ blur_bg_button.png
+ blur_bg_button_focus.png
+ drift.png
+ nitro.png
+ nitro_empty.png
+ pause.png
+ steering_wheel.png
+ thunderbird_reset.png
+ wing_mirror.png
+Copyright: Copyright 2017 Néd J. Édoire
+License: CC BY-SA 4.0
+Comment: Icons originally made for SuperTuxKart UI on Android.
+
+Files:
+ accelerator.png
+ accelerator_handle.png
+ accelerator_icon.png
+ gyroscope_icon.png
+ steering_wheel_mask_down.png
+ steering_wheel_mask_up.png
+Copyright: Copyright 2019 Benau
+License: CC-BY-SA 4.0
+Comment: License clarified/assigned in Jul 2021 via IRC.  accelerator_icon.png was committed in 2020, but is just a copy of accelerator.png with a square aspect ratio.

data/skins/cartoon/licenses.txt

@@ -8,9 +8,9 @@ Source: https://supertuxkart.net
 Files:
  glass_iconhighlight_focus.png
  bubble.png
-Copyright: ???
+Copyright: 2010 Dakal and/or Marianne Gagnon (Auria)
 License: CC-BY-SA 3.0
-Comment: From peach skin
+Comment: From peach skin, first found in commit 5cddb8ffb61001407ce97ee5a8c63faa18a08c2c.  It is unclear which author made these particular files.
 
 Files:
  src/Inter-UI-Black.ttf