Due to the use of the dataclasses mixin on the SQLAlchemy types, a
back_populates creates a RecursiveError when comparing two types. This
occurs because the dataclass will overwrite the __eq__ operator, and it
doesn't know when to stop comparing relationships.
Removing the dataclasses isn't the best approach, since then __init__,
__eq__ and __repr__ methods would have to be added to all types. Thus
the solution was to remove the relationship on the child (on a
one-to-one relationship) from the __eq__ operation, with the use of the
compare parameter.
Took the opportunity to define more logical __init__ methods on the
`Rule` and child classes.
Also revised the parameter options on some DB types.
`add` method replaced with `insert`.
`insert` and `select` implemented for new database base class.
Database unit test added.
Due to SQLite implementation of the primary key autoinc, the type of the
IDs on the database for SQLite changed to Integer.
https://www.sqlite.org/autoinc.html
