RenderMesh and MeshManager

For each Entity with a Mesh property, a RenderMesh is created.
For each mesh source, a MeshData is created.
RenderCommand has a handle to a RenderMesh. That allows for a RenderMesh
and MeshData to be properly updated if a Mesh's source changes.

Change-Id: I98d38c81e1049ba6e1549fd6a4b26b45f4ad40d4
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
MatrixManager

RenderNode now uses a QHandle to a QMatrix4x4

Change-Id: Ib1a239dc8b08e3da5d68f447e3ef6f3b8ddd2f0d
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>