Improve tooltip text and center tooltips

src/guiengine/skin.cpp

@@ -1849,7 +1849,7 @@ void Skin::drawTooltip(Widget* widget, bool atMouse)
     if (atMouse)
     {
         pos = irr_driver->getDevice()->getCursorControl()->getPosition()
-            + core::position2di(15, 15);
+            + core::position2di(10 - size.Width / 2, 20);
     }
 
     core::recti r(pos, size);

src/states_screens/options_screen_ui.cpp

@@ -151,7 +151,7 @@ void OptionsScreenUI::init()
     CheckBoxWidget* difficulty = getWidget<CheckBoxWidget>("perPlayerDifficulty");
     assert( difficulty != NULL );
     difficulty->setState( UserConfigParams::m_per_player_difficulty );
-    difficulty->setTooltip(_("Handicap stronger players in the kart selection"));
+    difficulty->setTooltip(_("Players can select handicapped (more difficult) profiles on the kart selection screen"));
 
     CheckBoxWidget* show_login = getWidget<CheckBoxWidget>("show-login");
     assert( show_login!= NULL );