RenderState reworked for OpenGL buffers

The OpenGL Buffer Object is now the central data store and they can
currently be connected to vertex data, texture data and framebuffers.
This is done automatically when connecting resources using the
RenderState::setMesh(), RenderState::setTexture(),
RenderState::setFramebuffer(), etc. functions.

The following classes are new/removed:

LibGem
=====
+ BufferState
+ VertexState
+ ProgramState
+ UniformState
+ TextureState
+ FramebufferState
+ Tracker

LibGem
=====
- Math (replaced by global functions in Mem::)
Merge branch 'master' of https://github.com/sunefred/Gravity3D