An ListEntrySource will be known to one ore more components
supporting the XListEntrySink interface, which all work with
this source. However, they will not own the ListEntrySource.
The ownership is with another instance, which may also decide to obsolete
the ListEntrySource for whatever reasons (e.g. because the data model
which the binding reflected died). For this reason, a ListEntrySource
must offer a possibility to be obsoleted by it's owner, and to notify this
obsoletion to other interested parties, such as XListEntrySinks.
