Allow Spaces to be archived

Summary:
Ref T8377. This adds a standard disable/enable feature to Spaces, with a couple of twists:

• You can't create new stuff in an archived space, and you can't move stuff into an archived space.
• We don't show results from an archived space by default in ApplicationSearch queries. You can still find these objects if you explicitly search for "Spaces: <the archived space>".

So this is a "put it in a box in the attic" sort of operation, but that seems fairly nice/reasonable.

Test Plan:

• Archived and activated spaces.
• Used ApplicationSearch, which omitted archived objects by default but allowed searches for them, specifically, to succeed.
• Tried to create objects into an archived space (this is not allowed).
• Edited objects in an archived space (this is OK).

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8377

Differential Revision: https://secure.phabricator.com/D13238