Make the interface to the Connectivity classes consistent

The main reason we need a consistent interface to Connectivity classes is so that a worklet can use a WholeCellSetIn argument to the ControlSignature and know how to operate the class. This makes the classes consistent and adds a regression test to make sure all the methods are working as expected.

An interesting upshot of adding these tests was that I discovered a bug in CellSetPermutation in that it works fine for point to cell, but is incorrect for cell to point. The solution is not straightforward, so I just changed the implementation to throw an exception.