Fix the testrunner to run tests
Store datetimes as utc timestamps

Django now uses a json session serializer by default which cannot store
datetime values, so serialise as timestamps.
pep8ify
Merge pull request #115 from mixcloud/pep8

pep8ify
Add signal fired when user alternative is set
Merge pull request #116 from mixcloud/user_enrolled_signal

Add signal fired when user alternative is set