Updated testsystems.py with multiple additions and additional options, mostly for dispersion correction control.
Fixed an issue with dispersion corrections and switching for water box.
Cleaned up issues with WaterBox subclass docstrings.
Removed __main__ from testsystems.py
Had trouble with the matplotlib part in .travis.yml, so removed it for now.
Merge pull request #121 from jchodera/testsystems-improvements

Updated testsystems with new tests, variants, and additional options