* Add Import actions on packages when smart import is available (no
conflict across packages)
* model validation is performed when wizard is opened
* imported schema is displayed, conflicts are in red
* Bos import: actions are not available for users (for now) -> packages
are always in overwrite.
* Update the viewer: a preview of the model after import is now
displayed
* A read only Action 'import' is displayed for none conflicting imported
content or for all imported content when SmartImport isn't possible.

[BST-551](https://bonitasoft.atlassian.net/browse/BST-551)