Blender Git Loki

Texture context selector for texture panel:
* Texture context was previously determined by going to the appropriate panel, for example "world panel -> texture panel" to access world textures. Additionally there was a separate button to access brush textures.
* Now the texture context can be selected directly through an expanded icon menu, which shows the available context options.
* This context selector is now at the top of the texture panel, but this could later be perhaps integrated to the context path somehow to be more intuitive.