Bug 550799 - Improve DataTemplate Editor reference handling

* Add a DataTemplate specific CreateNewModelElementStrategy which
forbids to add objects for non containment references
* Add a DataTemplate specific EObjectSelectionStrategy which only allows
objects from the same template
* Add RCPTT smoke test

Change-Id: I057c30f842d9a80fb1eed6b999312fd524d4c260
Signed-off-by: Eugen Neufeld <eneufeld@eclipsesource.com>
6 files changed