Investigate Simplifying Marray inheritance Heirarchy

It may be possible to eliminate PseudoMarray and other Pseudo<*> classes by having Marray inherit from Schema (and on down the chain, ImageSchema inherits from Schema, Image inherits from ImageSchema and Marray). The trick will be figuring out if it is straightforward to keep the correct shape visible (we want the one inherited from numpy to be used where it exists). I think this might work if we just inherit from Marray first, but it will need investigated.