Bug 495388 - [InformationModeling] ExecutionException when invoking
Create View action in Papyurs welcome page 

 - allow model creation only on Package
 - will allow only package selection in the explorer tree
 (some other element will still be visible)

Change-Id: I462eeb7a2488bca3020d91b5bebea2ab5f4c45c2
Signed-off-by: Benoit Maggi <benoit.maggi@cea.fr>