add notifications

[Mark Mikofski]

current: if new issues are made, nothing happens, even if app is loaded

proposed: app incorporates a service, that is started when the app is started. the service periodically checks for new issues, and if there is one (and the app is not started, or has died) then it will issue a notification.

[[https://play.google.com/store/apps/details?id=com.BreakingBytes.SifterReader&reviewId=03488945716726979032|suggested by tryangle on Google Play]]