Tests: be explicit about the tests directory

Although the natural environment for tests are UNIX-like systems, this
improves cross-platform compatibility so tests can also be run on Windows
machines. The change simply avoids the forward slash.
Docs: updated changelog after latest release
Cleanup: PEP8 fixes
Refactored retrieving the last revision number

Code was duplicated and this is code rather belonging to a model manager.
Cleanup: removed dead code