Tests improvements

Just some general changes to RatticWeb tests.

* Now uses Nose
* Now has --without-selenium option to runtests.sh that makes the selenium tests be skipped
* travis-ci Uses runtests.sh
* No longer require unittest.ExpectedFailure decorator for the creds.tests.test_password_generator test
* Pep8 and pyflakes ignore a static folder if there is one
* Only dodgy thing is introducing a condition in settings.py that depends on the existance of a ENABLE_TESTS environment variable