misc little changes
Avoid the use of the new GP editor as a cheating aid
Merge pull request #1286 from marcoll/master

Avoid the use of the new GP editor as a cheating aid
Fix crash when loading instanced node without texture.
Use half res FBO for SSAO

SSAO is a medium frequency effect, using half res fbo is fine and
improve performance and look by doing an additionnal bilinear filtering.
Also tune up some values.
Bloom: Use power of two quads.
Bloom: Tweak the threshold.
Bloom: Weight the different sized contribution.
Apply MLAA after color_in.
Fix too dark screen with MLAA enabled.
Add an option for Tex compression

Also turn m_ssao into bool.
Add some more graphic config options.
Handle skybox texture compression.
Fix a memleak
Add a config option to disable dynamic lights
Remove the ability to disable pixel shaders

It doesn't work with GL 3.1 and mesa drivers (which requires a core
context)
Try to fix additive blend for object
Merge branch 'master' of https://github.com/supertuxkart/stk-code
First pass to update video options menu
Fixed #1282: STK crash on startup for the first time.