Reference insertion, new and existing

Objectives:

* Split reference dialog (at least for now) an edit and an insert dialog
* Add reference search widget for selecting an existing source, or
  choosing to add a new one
* Abstract reference names, don't allow editing them and generate them
  when needed
* When editing groups, move the internal item and update all references
  to it
* Resolve name conflicts when moving a reference to a new group by
  generating a new list key

Bonus:

* Add getNodeGroups method to internal list
* Add getUniqueListKey method to internal list
* Add destroy functionality to ce.node to release events and references

Bug: 49733
Change-Id: Ib244ff6ad9b4cee1decfd9b9e1d3d4e9cdcfb78c
Merge "Reference insertion, new and existing"