Reset yaspgridentity.hh

After realizing that it is convenient to have a specialization
for codim dim (its the only entities that share ids with higher
levels in a globally refined grid), I want to revert the restructuring
hoping to preserve history. I fear my git skills were not sufficient.
Major overhaul / rewrite of the entities in yaspgrid

This is a first draft of an entity in yaspgrid. It is generic
for all codimensions and uses numberings of subentities which
follow the generic reference elements. This way Yasp will support
arbitrary dimension again. Testing of the code is still missing,
because some stubs have to be removed before changing the capability
hasEntity makes sense.