fix(river): add enabled col to river table, update on enable/disable of ...

...referenced entities

Fixes #6022 - empty river items fetched when referenced entities are disabled

TODO:
- [x] Make events private API
- [x] Fix Comments for Travis
- [x] Manual Testing
- [x] Automated Tests
- [x] Add the column to the install schema
- [x] Add documentation for property to model class
- [x] Export property value in toObject
I think if Travis is not blocking alignment issues, we should not block alignment issues. Let the tools do this dirty work for us. Instead, I've reported https://github.com/Elgg/Elgg/issues/7025.

In fact, I'd even prefer it if we got rid of this formatting check altogether and switched to a script which would fix it for us. We could run that as part of the release script to "true up" our style at every release, but wouldn't block on silly formatting issues which add roundtrips and waste contributor time.

But I digress...