Rename the class MonomLocalFiniteElement to MonomialLocalFiniteElement

Also keep around the old class with the old name, for backward-compatibility
until after the release of dune-localfunctions-2.4.
Rename class MonomFiniteElementFactory to MonomialFiniteElementFactory

Deprecate the old class, but keep it for backward-compatibility.
Test the new Monomial... classes instead of the old Monom... ones
Replace 'monom' in test file names by 'monomial'