WIP: IsFFEMatrix, IsFFEMatrixGroup etc. for MatrixObj

[fingolfin]

This is work in progress towards #3568. It is not yet ready in any form but I don't want it to get lost or forgotten.

[fingolfin]

OK, I guess the IsOrdinaryMatrix was here to avoid confusion about the meaning when applied to an IsLieMatrix (I think for MatrixObj we agreed that we only want "ordinary" MatrixObj; implementing Lie algebra elements, if desired, should be wrappers around ordinary MatrixObj. But I digrees)

So what do we do:

1. ignore this issue and just switch to IsMatrixOrMatrixObj (i.e., what this patch does right now)
2. Introduce a new filter IsOrdinaryMatrixOrMatrixObj and wire that in suitably, and use it here.
3. leave this DeclareOperation at IsOrdinaryMatrix and add a second DeclareOperation invocation, i.e.:

Suggested change

	[IsRing,IsMatrixOrMatrixObj,IsPosInt]);
	[IsRing,IsOrdinaryMatrix,IsPosInt]);
	DeclareOperation("CharacteristicPolynomialMatrixNC",
	[IsRing,IsMatrixOrMatrixObj,IsPosInt]);