Update to example materials

+ Added new brick textures
+ Added new wood textures
+ Added unlit black material
* Changed the default material textures so their colours more accurately
match their description
* Changed the shaders for the default materials to Mobile/Diffuse
* Changed the names for all materials and textures, except ones used in
code to use "scsg_NAME" so they can be distinguished from other project
materials and textures.
- Removed old materials and textures