minimize UI/X surprises around constellation create/delete/open/close and project add/remove

[abathur]

I don't necessarily think all of these are wrong as-is, but it's worth reviewing them as a group. These might need better defaults, or just more-explicit choices.

Probably fine as-is:

• Removing an open project from a closed constellation should not close the project.

Open questions:

• Should a newly-created constellation automatically open?
• If we add a closed project to an open constellation, should the project open?
• If we add an open project to a closed constellation, should the project close, the constellation open, or neither?
• If we remove an open project from an open constellation, should we also close the project?
• Should deleting an open constellation close the projects?

Potential changes:

• The open/close commands currently list the inverse set of open/closed constellations, but I could imagine some utility commands can can re-open an open constellation if some of its projects are closed (i.e., a bug caused them not to open, or the user manually closed them), or likewise the ability to forcibly close open projects in a closed constellation (a bug caused them to stay open, they were in another open constellation, or the user manually opened them).
• The menu option to "add an open project" should probably be disabled if there are no open projects? Or turned into an encouragement to open one?

Probable changes:

• Closing a constellation should only close a project if it is in no other open constellations.
• The menu should indicate which projects in a constellation are(n't) open. This will make it much easier for the user to notice some inconsistent state issues.