TEIIDDES-2172: Fixes problems with model definition editor

* Dispose method not called when editor is closed so resource change
  listener not necessarily removed from workspace. Therefore,
  MedResourceChangeListener created with defined hashcode so that only
  1 instance of listener added.

* When refreshing med, only refresh if the parent container has not been
  disposed.

* Editors for imported meds open as read-write due to eclipse links not
  persisting read-only attribute so brute-force their attribute.