Various statistics about revisions at /differential/stats/revisions/

Summary:
Show some statistics, like number of revisions, number of
revisions per week, lines per revision, etc. for phrivolous amusement.

Test Plan:
 - Went to /differential/stats/revisions/
Numbers seem right
 - Clicked 'Accepted'
Again
 - Changed to another user with long history
Load time was not too long though delay noticeable
 - Clicked 'Requested changes to'
User was preserved, looks good

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1643

src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php

@@ -96,6 +96,7 @@ class AphrontDefaultApplicationConfiguration
       '/differential/' => array(
         '$' => 'DifferentialRevisionListController',
         'filter/(?P<filter>\w+)/$' => 'DifferentialRevisionListController',
+        'stats/(?P<filter>\w+)/$' => 'DifferentialRevisionStatsController',
         'diff/' => array(
           '(?P<id>\d+)/$' => 'DifferentialDiffViewController',
           'create/$' => 'DifferentialDiffCreateController',