Added an initial tox config for easier local testing
Added config to test against PostgreSQL as well
Added Postgres environments to env-list
Worked around missing travis_ci_test DB preventing DB connection establishment during tests
add CONTRIBUTING.rst, associated tox changes
Merge pull request #36 from swisscom/postgres-testing

Postgres testing
Merge remote-tracking branch 'origin/master' into postgres-testing
Merge branch 'master' of github.com:swisscom/cleanerversion into prefetching-tests

Conflicts:
	versions/models.py
still messy, but more correct