Save saves markdown and updates the xml

Hook up the component delete button to the backend. Don't break if the process of updating a parent unit after deleting is interrupted (leaving a pointer to a missing module)

in order to avoid using stale modules when editing, clear out the @module variable after a save(). Then on a subsequent edit, it'll get recreated

always load in a new instance of the edit module. It appeared as though on multiple edits (w/o refreshing page) without creating a new data model, we were always referencing stale content from the previous edit

Make saving also save the children in the #sortable element (TODO: name the #sortable element better)

* NOTE: the new order is NOT saved to the server!