Receive native OS push notification alerts

[devinbileck]

The Bisq application is able to be configured to send native OS push notifications of important events to a paired mobile app. This is the only functionality of the existing mobile app and we should be able to implement the same behavior with minimal effort.

Note that this relies on Apple's APNS service for iOS and Google's FCM service for Android and will not work on some custom Android OS's that do not provide Google Play services such as CalyxOS or GrapheneOS. An alternative approach will need to be implemented to support those and is outside the scope of this task - see #7.

We should be able to utilize the existing mobile relay node to send iOS and Android push notifications without any changes required to the service.

Todo:

• Receive and display notifications of the following events:
  • price alert
  • new offer
  • offer taken
  • trade status changed
  • dispute message