AutoTableNameMeta enhancement: automatically detect when single table inheritance is used

[ods]

Right now user has to specify __tablename__ = None to disable setting new name. SQLAlchemy extension to Flask does simple check to see if class dictionary has columns with primary_key set to True. This checks doesn't cover all possible cases, but works for the most used one.

Cases where Flask fails:

• Columns properties
• Composite properties
• Declared attributes
• Primary key defined in __table_args__

Some of them are important to us since we use factories that wrap all collumns.

It's not obvious how to handle classes that inherit primary key from abstract class (__abstract__ = True).