Add database support

[ItsDrike]

We'll definitely need a database for the bot as we go on, we'll need to add support for it. Most likely, just using sqlite will be enough here and it will make it a lot easier for everyone involved when compared to having to work with a full dbms, like postgresql.

Question is whether or not we'll also want to do ORM (sqlalchemy) or just write some simple crud classes, or work directly with SQL everywhere. As much as I like sqlalchemy, it's probably a bit too involved and complex for us now. As for writing SQL directly, that could lead to issues and is probably more complex than just exposing some basic crud classes that everyone can use even without being familiar with SQL.

[ItsDrike]

After some discussions, we'll go with SQLAlchemy after all, mainly due to the possibility of using alembic for db migrations, which would be pretty annoying to have to handle manually. For the backend, we'll still go with sqlite though, to avoid everyone having to have a database that can can connect to.