Allow for import of MDL defining model relationships

[matthewhegarty]

Is your feature request related to a problem? Please describe.

I am a new user and I found that it could be cumbersome to create relationships between model entities by hand.

I asked on Discord whether it was possible to import relationships via JSON. Since I use Django, it may be possible to export from Django model to a JSON format which defines the relationships, this would save the manual effort, and would allow for some synchronization to handle model changes. Similar tools could be built for other frameworks and DBs.

There is a model descriptor (MSL format) which could be used.

Example JSON.