Fix rating notification for multiple conferences

[abhinayagarwal]

The way rating works now is that when the user selects a conference, it sets a local notification to remind the user to rate the app at the end of the conference. Once the notification is delivered, the user is taken the Sessions view when they tap on the notification.

The end of the conference can be days or weeks away. If the user switches conference in between this time, the rating notification will still be delivered, but the user taps on the notification, the session view won't show a rating dialog. The dialog will be shown if the user switches and goes back to the conference for which the notification was delivered.

This is because the show rating logic and notification logic are different.

We need a way to fix this.