Make clicking on a presence list name narrow you to those PMs.

This parallels clicking on a stream name, which narrows you to that
stream. This also gives you a discoverable way to narrow to PMs with a
particular person.

(imported from commit 6c706f0643f6a8ec20ac38360153227ec2f645ae)

zephyr/static/js/ui.js

@@ -1245,6 +1245,7 @@ $(function () {
 
     $('#user_presences').on('click', 'a', function (e) {
         var email = $(e.target).attr('data-email');
+        narrow.by('pm-with', email, {trigger: 'presence list'});
         compose.start('private', {private_message_recipient: email,
                                   trigger: 'presence list'});
         // The preventDefault is necessary so that clicking the