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.
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
Fix #1484 (crash on windows in release mode).
Init texture only once, not each frame
Fix build on travis
Fix transparents
Remove Base Vertex/Offset if base instance is unavailable
Implement runtime detection of srgb bindless fix
Use ATI instead of AMD in vendor name.
Use uvec2 instead of sampler2D
Check if user config dir exists
Add some compile time check