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
I tried to make queries, that took user input, into prepared statements. The insert and update queries appeared to be the only functions that insert user input into the database.

There is ``insert_failures()`` in ``framework/database.py`` but it is only called when an issue occurs by Freeseer.