Switch to sqlite for session and interaction data storage

[philip-ulrich]

The idea being the longer you run the bot - the more inefficient the json storage becomes. sqlite will fix this - but we need to seamlessly handle the switch and allow a manual export/import to/from json if needed.

@S0yKaf is already working on it here: https://github.com/S0yKaf/Insomniac/blob/experimental/src/database.py