Replace databaseInterface with Django models

~~`databaseInterface` is still imported in a few places in MCPServer, primarily for the `getUTCTime` function that will be moved elsewhere, and for database locking that may be removeable.~~

See comments below.
Turns out there was a much smaller surface area of stuff to change here than I thought, and it's definitely better to be consistent at this point, so made the changes everywhere there wasn't much restructuring to do so.