member_of field on items still show all nodes

[bseeger]

If we have time to fix one angle of this, then fixing #108 will be of higher benefit as it will provide pre-save validation and cover both the UI and ingest workflow paths.

The member_of field is an Entity Reference field that will show all the nodes in the system, regardless of whether or not the user can edit them. Ideally this member_of field will only allow nodes that the user has edit permission on.

This can manifest a weird scenario where a user can add a node to any collection in the system, regardless of whether or not they have permissions to edit items in that collection.

Here is one thing I tried to do to fix it, but wasn't able to get it to work: https://docs.google.com/document/d/12UBsXPWy9lG8owxg2cAA7ixxoqLgAi0oK1pSZoZSEWQ/edit#bookmark=id.iq5sjmhj3kw1

In theory this method should work, but after trying for a while, I couldn't get it to work and I needed to move on.