[wrapper] Merged the two EclipseParticipantFactory subclasses
[ModelObject] (Slightly) increased the visibility of the extended data map

This commit also removes the unused pair of getExtendedDataKeys methods
[ModelObject] Added a change descriptor for moving extended data

This is a very, very experimental change descriptor, so its visibility will
remain package-private for a while
[ModelObject] Added validation and execution for the new move descriptor
[IChangeExecutor] Deleted IChangeExecutor

All implementors of IChangeExecutor have been deferring to ExecutorManager
for a long time now; this commit recognises that change
[Signature] Use the namespace to retrieve named controls

This fixes an occasional bug caused by the lack of name normalisation
Removed a few rogue references to IChangeExecutor

This commit also renames the "target" parameter of ChangeCommand to
"context" to reflect its changed function