Added rotation properties for GLMesh

GLMesh can now be rotated from the sc file using rx,ry,and rz.
Moved camera start height higher
global replace of \returns to \return
GLMesh changes

minor changes for formatting and comments, GLMesh is now in Sigma namespace, etc.
most significant change has to do with shaders. Instead of a reference to the static GLIsoSphere shader, each
GLMesh may reference a different shader using mesh.LoadShader(name).
Merge remote-tracking branch 'upstream/develop' into formatting

Conflicts:
	src/systems/OpenGLSystem.cpp