Generic cross tables dont play nice with django

[miketynes]

Question from @vshekar: do we want property_x to have a generic foreign key?
Potential answer: no -- having one property_x minimizes effort from a psql implementation perspective but not from a django perspective. aside from minimizing effort, we cant think of any advantages

One way to do this in django: https://stackoverflow.com/questions/54217937/how-to-bind-multiple-models-to-one-manytomanyfield

Opinion piece on why not to do this in django: https://lukeplant.me.uk/blog/posts/avoid-django-genericforeignkey/