When rendering opaque (RGB-only) windows the alpha ends up to be 0
with blending disabled. This breaks subsequent rendering steps which
require blenden (e.g. Lanczos). Therefore a uniform is used to ensure
that the alpha channel is set to 1.
Adds a shader to render an untransformed scene. renderGLGeometry is not used any more and replaced by generated triangles stored in a GLVertexBuffer.
The GLVertexBuffer has a new attribute to decide whether a core profile compatible rendering has to be performed.
Currently windows and EffectFrames can make use of the new shader.
The shader contains a debug mode which colours all rendered fragments in green. It is currently enabled in scene_opengl.
Rendering transformed geometries (without shader) is currently broken.
