Fix bug in model loading code

I was assigning a reference to a temporary! How did that not crash? Fix
is to add a reserve function to the InterleavedBuffer so we can expand
it instead of trying to re-assign some reference.
Make use of reserve for resizing the render batch
Trying to track down a state-stomping issue

Seems to fix by unbinding the VAO after setting indices but I'm not sure
that's the proper fix, should find who's actually stomping. Also fix
improper ordering of binds in model loading which would mess up state of
the currently bound VAO. Fix is to bind the model's VAO prior to
loading and doing any binding of vbo & ebo
Not sure why I need separate branches here anyways