2 Reminders to myself or whoever else ever looks in here...
4 SQLite needs some heavy refactoring, the subroutines are becoming too complex to understand easily.
5 MySQL needs implicit FK support, I think.
6 Need tests for left_base_classes, additional_classes, additional_base_classes...
9 If local column is UNIQUE or PK, use has_one() for relation?
10 Re-scan relations/tables after initial relation setup to find ->many_to_many() relations to be set up?
11 Check NULLability of columns involved in the relationship, which might suggest a more optimal non-default -join-type?