[common.float_cmp] add float_cmp() as in pyMOR
[common.float_cmp] add float_cmp() as in pyMOR

This implementation for float_cmp works better for me in a lot if places.
We should use it in the other implementation in the long run...

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