Moved all Mesh and derived resources into resource namespace

Also renamed texture and mesh load methods to Load() to be inline
with coming design changes.
Renamed GLTexture to Texture

Also did some spaces to tabs cleaning, typos, and removed redundant Sigma::
Changed to using shared_ptr for textures
Added ResourceSystem

To make an item a resource it my have a static TypeID member and provide a
bool Load(std::string) method. Then simply tell the ResourceSystem to CreateResourceLoader<MYRESOURCE>()
and you get then get resources of that type.

Texture now generates an ID in the constructor.

Several spots are using  __declspec(selectany) for static class members to create them in the header. To quote the gcc manual
"The selectany attribute is only available on Microsoft Windows targets. You can use __declspec (selectany) as a synonym for
 __attribute__ ((selectany)) for compatibility with other compilers. "
So it should be safely ignored unless under windows.