Concrete quantum database

Issues with current Quantum DB implementation:
Plugin schemas and core schema share same SA Base object
Plugins can't version DB separate from core schema
Each plugin can change the core schema if they use it
Plugins may not even use or populate the base quantum schema
Certain failures don't rollback correctly, leading to bad data
Plugin schemas are incompatible

Proposal:
all plugins should use a common engine
each plugin should maintain a separate db base object

Having a concrete core database in quantum gives us the ability to reliably use it outside the plugin. Not sure how to solve plugin not populating the db.