Extract user_events.js.

This moves people.update() to user_events.person().

We now also use user_id as the key for finding person
objects in people.js (instead of email).

zproject/settings.py

@@ -834,6 +834,7 @@ JS_SPECS = {
             'js/server_events.js',
             'js/zulip.js',
             'js/activity.js',
+            'js/user_events.js',
             'js/colorspace.js',
             'js/timerender.js',
             'js/tutorial.js',