Host hardcoded in creation of sqlalchemy engine

[egillax]

I think in general the sqlalchemy.create_engine needs to be revised. To get it working for me I used:

engine = sqlalchemy.create_engine(f`postgresql://{config.user}:{config.password}@{config.host}/{config.dbname}`, echo=False)

Then I added user, password and host to the config file.

Might also be worth refactoring the engine creation and session execution out into a separate function since it's included in multiple functions and is always the same (that I've seen so far)

[cxji]

Thanks for suggesting the refactoring! Since it seems like how the engine is specified depends on how the database is set up, I added a create_sqlalchemy_engine function to config.py for users to specify how to create engines for their set-ups.