unit test and refactor database.py

Updates to ``tests/framework/test_database.py`` and ``framework/database.py``.

- Replaced ``test_database.py`` ``unittest`` references with ``pytest`` references
- Removed test methods that checked the return type of database functions
- Added test methods that checked the return values of database functions
- Modified database functions to handle python strings properly
- Added bound values to the add_presentation and update_presentation database functions.
- Removed dummy record inserted by default.

Related gh484
If there are end users running older versions of the client then it could be useful to test that their databases upgrade correctly when they get a newer version of freeseer? Although I am not sure how many people actually run freeseer with a very old version like 2x