I should be able to limit the sharing scope of an App I create

(User Story, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Apps
Summary: Currently, all Apps are created as Public. Ideally, I should be able to create one and just share it with my friends, or even just for myself.
The key detail is in Extractees.computeExtractees; this has PublicTag hard-coded for the moment.
In principle, fixing this is easy. But the UI work is far more than the back end, and we need to think through the UX.