[TIMODOPEN-292] Adding PushNotifications.query method

#### Steps for testing:
1. Run the example app with the ti.cloud modules.
2. Go to `Users` and login.
3. Got to `Users` > `Query User`, select the user that you are currently logged in as, click the `Copy User ID` button.
4. Go to `Push Notifications` > `Settings for this Device` and enable push notifications (must be done on device not sim).
5. Go to `Push Notifications` > `Subscribe` and subscribe your device (must be done on device not sim).
6. Go to `Push Notifications` > `Query Subscriptions`.
7. Paste in the User ID that you copied in step 3. 
8. Click `Query Subscriptions`, you should see your subscription show below the button.