[new feature] Post processing effects

Hello everyone 
I have implemented a basic post processing shader to allow 3DĀ artists to tweak the output of stk engine.
How it works ?
You take a screenshoot of your track in game and you tweak the levels in gimp or photoshop.
Then you copy the values in the color correction box in blender

Here is an example of what you can do

(before/after)
The effect is only applied to the 3D rendering. The GUI (nitro bar, icons, etc) aren't affected
This feature is still WIP. Currently color grading isn't supported. I will implement that when I have the time to do. If you want to test this feature, you need the last trunk revision + the last exporter revision. The trunk version is very unstable (since we are merging the GSoC branchs).

I have implemented a basic post processing shader to allow 3DĀ artists to tweak the output of stk engine.
How it works ?
You take a screenshoot of your track in game and you tweak the levels in gimp or photoshop.
Then you copy the values in the color correction box in blender

Here is an example of what you can do

(before/after)
The effect is only applied to the 3D rendering. The GUI (nitro bar, icons, etc) aren't affected
