Projects - tighten up a few things

Summary:
Fixes T2675, T2676.

 - when the last person leaves a project it is archived.
 - a script to archive all memberless projects
 - better feed stories for the various policy edits you can do
 - phriction pages are also moved as you rename projects

Test Plan: edited some projects and noted reasonable feed stories. ran script against test data and it worked! left a last man standing project and it archived. renamed a project to "a" then "b" then "a" (etc) and it worked including phrictiondocument moves

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2676, T2675

Differential Revision: https://secure.phabricator.com/D6478