Encapsulate fbos in a class
Move final blit to render.cpp
Reenable splitscreen
Attempt to fix travis ci
Create RTTs only when loading a track
Use rtt with fitting size.
Width and height are passed by UBO
Fix dof and transparent fog.
Few more checks for assets
Install assets in data directory
Fix displace effect.
Merge branch 'fboencapsulate'
Add a fake skybox where no skybox is available

For spheremap shaders
try to fix linux compilation
Revert to spheremapped reflection
Use correct mapping for spheremap
Fix texture sampled by spheremap
Spheremap: Flip y and add light.
Fix kart shadow vs kart animation (for the main player only)
Try to fix linux compilations problems (apparently on some systems
Screen is defined, which then interferes with out Screen class).