Improve browsability of Projects query

Summary:
Ref T5750. Same deal as D12427, but for projects.

(As before, mostly making the empty/browse view work instead of return nothing.)

Test Plan:

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5750

Differential Revision: https://secure.phabricator.com/D12428