[488386]  Boundary conditions for generation launch configurations

- Add checking on the existence of the property on the model.
- Add checking on the existence of the launch configuration for a given
stored property.
- As now, only the launch configurations configured for the given model
are retrieved in the properties page.
- A message is displayed if no launch configuration or no selection. 

Bug: 488386
Change-Id: Ia558e91b3039c6186bd0ad787e3047fc21da7ec2
Signed-off-by: Cedric Notot <cedric.notot@obeo.fr>
3 files changed