title: Update DB when Google Calendar Event change
body: <p>I have been implementing some functions of google calendar api. I have a custom calendar which have the capability to sync with google calendar. This means, you can create, and edit calendars and events from my dashboard to google calendar account. The main problem I am facing is, if I update the event directly from my google calendar. I have implemented push notifications and getting response like this:</p>
  
  <pre><code>    {
        "Google_channel_ID": "19835150 - 0057 - 11e6 - bc9c - 1735798 ca540",
        "Google_channel_token": "calendar_id = 4e7 d5c20ht9lpfdtuukcsvgeq4 @group.calendar.google.com &amp; user_id = 43e d7rxeqqce3fk09ahszc",
        "Google_channel_expiration": "Tue,12 Apr 2016 12: 34: 36 GMT",
        "Google_resource_id": "oLMEEhHAw5Xo3r2187CWykjAtm0",
        "Google_resource_URI": "https: //www.googleapis.com/calendar/v3/calendars/4e7d5c20ht9lpfdtuukcsvgeq4@group.calendar.google.com/events?alt=json",
        "Google_resource_state": "sync",
        "Google_message_number": "1"
     }
  </code></pre>
  
  <p>But this response is very general. For example, If I have 1000 events on this calendar, and update the complete 1000 events. I will receive always the same notification 1000. I would like to know, if it is possible to get which event id has change, so I can perform and update to my DB.</p>
  
  <p>The way I init the watch is like this:</p>
  
  <pre><code>    exports.watch = function(req, res){
         var channel_id       = uuid.v1();
         var user_id      = req.body.user_id;
         var calendar_id     = req.body.calendar_id;
  
         authorize(user_id, function(oauth2Client){
            var data = {
               auth: oauth2Client,
               calendarId: calendar_id, 
               resource: {
                  id: channel_id,
                  token: 'calendar_id='+ calendar_id + '&amp;user_id=' + user_id,
                  address: 'https://api.medradr.com/google-watch',
                  type: 'web_hook',
                  params: {
                     ttl: '36000'
               }
           }
        };
        calendar.events.watch(data, function (err, response) {
            if (err) {
                console.error('The API returned an error: ' + err);
                return;
            }else{
                res.send({ok: true, message: 'Listener created', result:response}); 
            }
        });
      });
     }
  </code></pre>