Add an "active login sessions" table to Settings

Summary: Ref T4310. Ref T3720. Partly, this makes it easier for users to understand login sessions. Partly, it makes it easier for me to make changes to login sessions for T4310 / T3720 without messing anything up.

Test Plan: {F101512}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3720, T4310

Differential Revision: https://secure.phabricator.com/D7954

src/applications/base/controller/PhabricatorController.php

@@ -44,7 +44,7 @@ abstract class PhabricatorController extends AphrontController {
           'SELECT u.* FROM %T u JOIN %T s ON u.phid = s.userPHID
             AND s.type LIKE %> AND s.sessionKey = %s',
           $user->getTableName(),
-          'phabricator_session',
+          PhabricatorUser::SESSION_TABLE,
           'web-',
           PhabricatorHash::digest($phsid));
         if ($info) {