Changed tiles logic

- Fixed possible NullReferenceExceptions in the Background agent
- Moved some tuff into own library to allow sharing it with the
background agent class
- Changed tile updating to run fully on the phone
- Changed primary tile to support wide tiles:
! Still needs a medium and small icon
- Known issue: The constructor deletes the tile images for debug
purposes. A debug build will not have back background images after the
background task has run. This behaviour is not present in release
builds.
- Moved notification formatting into own helper class
- In app notifications are now full text if only one notification is
present