Add support for forein keys in schema generation within aggregates

[schauder]

#756 introduced Liquibase based schema generation, but it ignores foreign keys. This issue should change this.

We should:

• create the back reference pointing back to the parent entity.
• create the key column for List and Map typed properties.
• create appropriate indexes and constraints for these columns.

[pschijven]

Hi @schauder, if this issue is not time-critical, I would be happy to help out with this one.

[schauder]

Great, go ahead. Let me know if you need help.

[pschijven]

Hi @schauder, I suddenly received a short project at work, so at the moment I'm unable to spend time on this issue.

If it is still open in about 2 or 3 weeks, I'd be happy to continue with it.

[kobaeugenea]

Hi everyoune!
@pschijven As you didn't work on it for some time I created pull request. Hope you don't mind.
@schauder Could you please review it and if it seems okay, I would be happy to work on #1600.

[pschijven]

Hi @kobaeugenea, no worries! 🙂