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
Since it more or less covers the same tests as the other two methods (it currently differs a bit from `test_update_fake_presentation` but can be modified to do the same) then I don't think there's a compelling reason to keep the other two tests since that stuff is tested already here.