ENHANCEMENT: #7 More optimization output

stdout/stderr of subprocess.Popen is redirected.
wrapping.py accepts 2 new arguments, if none is set
the default behaviour is to only print stderr.
Arguments are:
--silent:  Nothing is printed
--verbose: stderr/stdout is printed
All output is still written to a file.

Minor Changes:
Calculation of duration of HPOlib/optimizer/benchmark
in wrapping.py. Fix imports and bugs, clarify exception and output.