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 added ``assert False`` and it appears like they were not actually getting called (no wonder running tests sped up on my computer...). I have called the nested tests now. The reason they're nested is so the decorator can be used. With the httpretty decorator it is not possible to pass a fixture since it expects no arguements in the decorated function.