White space fixes/ relative imports/ add __repr__ for ss

These are all the changes necessary to bring the jgoppert github and
python-control github branch in sync. The changes have all been
hand merged. The changes are primarily pep8 white space and other
formatting fixes. The imports were also changed to be relative imports
and __repr__ was defined for state space systems. I also skipped tests
that weren't working and put a warning message.