Primitives cleanup, part 2: unified OBJ and builtin primitives as much as possible.

Use index buffer in both cases now.
Also disabled depth sorting, probably not used and needs re-lock of index buffer.
Primitive cleanup: implemented RotAndTra accessors in terms of the more descriptively named ones to avoid code duplication.
Primitives optimization: most transformations are now handled by the world transform matrix.

This allows us to change these transformations without re-locking the vertex buffer,
avoiding a pipeline stall.