[Work in progress] Restructure test suite

- [x] Rewrite tox to use multi-dimensional
- [x] Use pytest and pytest-django as test runner
- [x] Rewrite travis settings to use tox
- [x] Separate tests into different files instead of one huge tests.py

**Todo:**
- [ ] Make sure vagrant tests still work
- [ ] Fix dbm tests
- [ ] Fix pgmagick tests

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I know this is a large diff, therefore there are no large changes to the tests. They are only moved and new hashes were needed in some of them.