Meta: DipDup ORM

[droserasprout]

Missing features

• Support for composite PKs.
• One-to-one and one-to-many relations in a single model (possibly works already)
• Basic TimescaleDB integration
• Better __repr__ for project models #482
• Global transactions

Bugs

• update_or_create Tortoise call fails with TransactionManagementError #236
• Fields with null=True are typed incorrectly

Other

• ForeignKeyField definitions should refer a single class, w/o strings
• A (much) stricter QA -- linting, typechecking etc.
• Drop ugly MySQL hacks