AADL Navigator: Add node that shows project dependencies

[lwrage]

The node should expand direct project dependencies. Operations should allow adding and removing dependencies. (Undo!)
Could use drag and drop to add dependency. (Check for cycles!)
child of #1371

[lwrage]

For AADL projects only.

[lwrage]

Simpler approach for editing project dependencies:
Add context menu to dependencies node ("Modify dependencies...") that opens the corresponding project properties page.
No DnD

[AaronGreenhouse]

1. Just show the depended upon projects.
2. Allow editing of dependencies

[AaronGreenhouse]

Done. Added a virtual node for the depended on projects. It only shows if there is at least one. Added an action to the navigator context menu to edit the project dependencies. This action is active on the virtual node and on AADL projects.