Parent blueprint not added to nativization array if only child saved

Currently parent blueprints are added to the list of blueprints to nativize if their children are flagged to be nativized only if they are also individually saved.

Ideally, we'd update the list of blueprints for nativization with the parent when the child itself is saved to prevent problems from arising when saving only the child blueprint. (I.e. user may flag child for nativization, then save it and close out of the editor while not wanting the other changes they've made throughout the session and therefore not saving the other assets on close.)

Found on //UE4/Release-4.15 CL-3269047

1. Open UE4Editor.exe QAGAME
2. Open Project Settings -> Packaging
   1. Set Blueprint Nativization Method to Exclusive
3. Create a Child blueprint of QA_TestHelper, open it.
4. Select 'Class Settings' in the blueprints tool bar
5. Check 'Nativize' in the class settings.
6. Compile and save the child blueprint.
7. Go back to Project Settings > Packaging
8. Expand the 'List of Blueprint assets to nativize'

Result: Only the child blueprint has been added to the array for nativization.

Ideal: On save we update the array with the entire list of those waiting to be added (i.e. the parent as well.)