Feat: backend database management API

[danphenderson]

Add management class to app.core.db.py.

• implement table loading, which registers a data-orchestration/event (before registering, look up pipeline by name, if it doesn't exist, then post new pipeline)
• management of db should be agnostic of the models.py and schemas.py (except for BaseModel and BaseSchema).

Stretch:

• Add superuser auth on endpoints
• Create app.base.py and move base model and schemas

[danphenderson]

Gut tells me that an 'app/base.py' will create a cyclic dependency.