Privately shared applications can be publicly shared by any user

[greenfeld]

Privately shared applications can be publicly shared by any user, or so the GUI seems to indicate. The new public status icon is not copied to other users of the shared activity instance though.

Reproduction:

1. Start a sharable activity such as HelloMesh on laptop A.
2. Have A send a private invitation to laptop B from the Network View to join the activity, without publicly sharing the application.
3. Have B join the application.
4. Either A or B now can attempt to publicly share the application, and this fact will not appear on the other laptop. Laptop A sharing the application definitely makes it appear in the Network View on other XOs not currently in the sharing group.