Revert "Revert "[common.vector] added float_cmp""
Revert "Revert "[common.vector] added float_cmp""

This reverts commit 3930c9f46623f4f0c92f240bdde001920514b6a0.

Obviously, Dune::FloatCmp compares scalars, and not vectors.

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