[Spike] Investate push notification channels

Overview
Implications of changes
Creating a notification channel
Creating a notification channel group
Creating a notification
Reading notification channel settings
Updating notification channel settings
Deleting a notification channel

Main links reviewed:
https://developer.android.com/preview/features/notification-channels.html
https://medium.com/exploring-android/exploring-android-o-notification-channels-94cd274f604c
https://code.tutsplus.com/tutorials/android-o-how-to-use-notification-channels--cms-28616
https://stackoverflow.com/documentation/android/10018/notification-channel-android-o#t=201707271144370329859

Spike findings in .md here: https://drive.google.com/open?id=0B7Kf5uuSRetJa2xiZF9VSFJMYzQ