Glow Tiles:- Added texturing to tiles. Don't bother getting the shader variable locations, as we've specified the positions in the shader (see VertexAttributes.h).
Glow:- Texture, added SetDefaultSamplerAndWrap which is useful to call after creating a texture. A texture needs a sampler and wrap before it will be rendered.
- TextureUnits, fixed unbinding of textures not being removed from the map, so that re-binding it would fail.