Sync app settings via backend service (e.g. using Google account)

[greentux]

Shold be possible to share data across devices via google account (like many other apps do so). No need of own synchronisation server etc. Same count = same config :)

[johan12345]

Related to #85.

Sync via Google Account (i.e. data stored in Google Drive) could be a relatively straightforward solution, however we have to keep in mind that this would only work on devices with Google Services, so the F-Droid version of the app would not be able to use it.

[johan12345]

Documentation: https://developers.google.com/drive/api/guides/appdata, https://googleapis.github.io/google-api-java-client/android.html