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
from the database schema ``UNIQUE (Speaker, Title) ON CONFLICT IGNORE``
It is not, ack.

How can we then pull out a presentation from the database if all of the fields can collide except the ID? In the source code we have access to only the presentation fields that can collide with one another and no access to a guid associated with a presentation. I will think about this.