Add a Join / Leave button to Projects

Summary: Make it easy to join or leave (well, slightly less easy) a project.
Publish join/leave to feed. Fix a couple of membership editor bugs.

Test Plan: Joined, left a project.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T681

Differential Revision: https://secure.phabricator.com/D1485

src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php

@@ -207,6 +207,8 @@ class AphrontDefaultApplicationConfiguration
         'affiliation/(?P<id>\d+)/$'
           => 'PhabricatorProjectAffiliationEditController',
         'create/$' => 'PhabricatorProjectCreateController',
+        'update/(?P<id>\d+)/(?P<action>[^/]+)/$'
+          => 'PhabricatorProjectUpdateController',
       ),
 
       '/r(?P<callsign>[A-Z]+)(?P<commit>[a-z0-9]+)$'