Alpha version of a track info screen (instead of a dialog).
Forgot to actually add the new files :(
Made more space for credits that span more than one line.
Siwtch left and right side of the top screen.
If minimum or maximum is set for a spinner widget, automatically
adjust the value if its too low or high.
Removed old track info dialog, fixed crashes in track info screen
(caused when making some spinners etc. visible).
Merge remote-tracking branch 'origin/master' into gui_screen
Use header font for title, removed second 'back' button.
Implement AZDO
Fixed path to data directory on linux.

Ideally we should use relative paths, which could make possible to run the game after using:
make install DESTDIR=./any/local/path

I also added path to "supertuxkart-assets" directory, which cmake already search.
Removed unnecessary include.
Fixed setting of actual number of laps of a track; cleaned up docs.
Fixed crash: m_tracks is NULL, and can't be used to get the default
number of laps here.
Add instanced spheremap shader
Add instanced detail shader
Add unlit instanced shader
Do not split animated mesh from static list
Fix spheremap shader
Use one call for each shadow cascade instead of a big one.
Factorise AZDO related code
Free texture memory when an object is destroyed