Added methods to release GL textures, misc fixes
Added elapsed time control in flushDeletedTextureObjects
Added unit test to TextureManager, fixed bad access in release loop
Merge pull request #166 from jtorresfabra/releaseGL

Fixes for TextureManager and releaseGLObjects
Moves pixel configuration into Texture class

The problem is that using flipy for prepared cubemap is not
suitable. Moving the configuration in texture level let the user to
choose what he prefers. By default for texture y flip is activated, but
for texture cubemap by default it's false.

Conflicts:
	sources/osg/Texture.js
Adds pbr sample
Setup initial sample with environments
Adds model and reorganize sample code
Adds texture unito 0
Should work with based importance sampling but it does not
Test importance sampling
Needs now to filter correctly the lod
Uses roughness on multi texture because of lod issue
Add a new model and configure the environments
Fixes camera position
Adds new model from allego
Adds template scene with metallic materials
Adds environments
Adds glsl texture function to use prefiltered environment
Adds script to build ibl