Made MappingQ aware of Manifold

This is the last step that was necessary for the Manifold branch. 

With this modification, MappingQ, when constructed with the optional flag `curved_interior_cells`, will obey what manifold says for all interior support points. 

This version is fully compatible with the old Boundary classes.
Is the number of G-L points dependent on the order of the mapping? If so, can you add a sentence to this effect? Otherwise, the object could be static.