Support new IDM schema API for custom relationships and potentially other schema mods

[vscheuber]

Frodo Library should support the new IDM schema API for custom relationships and potentially other schema mods.

[vscheuber]

When to use the new schema API:

On export (NO NEED for new schema API):

• managed.json contains custom relationships
  • export both:
    • managed.json
    • repo.ds
• managed.json does not contain custom relationships
  • export only managed.json

On import (NO NEED for new schema API):

• managed.json contains custom relationships
  • import both:
    • managed.json
    • repo.ds
• managed.json does not contain custom relationships
  • import only managed.json

When managing (CRUD) individual custom relationship attributes:

• use new schema API

Frodo-Lib doesn't support CRUD operations on individual MO properties, today. If that kind of functionality is added, the above should be considered and followed. Removing 2.0.0 label.