[common.ranges] add support for dune-fems grid parts
[common.ranges] add support for dune-fems grid parts

This commit allows to call entityRange() for a either a grid view or a grid
part. In addition I renamed ViewRange -> EntityRange and
viewRange() -> entityRange() which is consistent with the existing
intersectionRange() and cornerRange()...

renemilk/DUNE-Stuff,renemilk/DUNE-Stuff,renemilk/DUNE-Stuff