Evaluate tox to automate and standardize testing

[giffels]

Together with #176 it should be evaluated to use tox to automate and standardize testing in TARDIS. Since the current procedure is going to be deprecated soon.

python setup.py test                                                                                                          
running test
WARNING: Testing via this command is deprecated and will be removed in a future version. Users looking for a generic test entry point independent of test runner are encouraged to use tox.