Migrate: Push notifications

IMPORTANT: You need to re-add the site in the app, sites already stored will cause problems. That's because in some cases the URL used to set the siteID was not the same as Moodle uses, so the site IDs don't match. Please look at this commit . Access the app as studentjuan in prototype 2.9 (both in the app and in browser). In browser, send a message to yourself while you have the app in foreground. Check that after a few seconds a notification is shown. Do the same again with the app in background. Check that the notification is shown too (should be shown faster). In both cases, check that clicking the notification sends you to the discussion list. The new message should be shown in the list. Do the same with a notification and check that clicking on it sends you to notification list. Logout in the app, access as another user and check that you still receive push notifications from studentjuan. If you click to a notification from studentjuan, the app should login you as studentjuan and redirect to the right state.