Push notification settings

[nickoneill]

We now have a couple different ways to get info via push notifications, one is new issue alerts and the other is new inbox messages. We don't have a good way for people to opt into one but not the other but we could pretty easily with a notification settings page.

• Rename the reminders settings screen into Notifications
• Add two new toggles, one for issue notifications, the other for new inbox messages
• Add a message to let users know if push notifications have been denied on the top of this screen
• If a user arrives here and turns one of these on without having push notification enabled, we should ask for permission when they toggle on one