Fix EZP-22260: As legacy User I want node assignment remote id to be kept on publish

This PR resolves issue https://jira.ez.no/browse/EZP-22260

Remote id is now always generated for new node assignment and set to the node on publish.
Also hidden and visibility statuses are now set on node assignments and copied to node on publish.

Additionally this fixes node edit form:

* sorting for added nodes is always set from corresponding content class
* already selected nodes are disabled in browse mode
* it is possible to remove nodes and add them again
* visibility selection is fixed