Support localized notifications

[Lineflyer]

Up to now only standard notifications are localized but custom notifications are only possible in one language.

It should be possible to push self created notifications (not including message_id for localisation in cgeo) in several languages.
Depending on the locale of the device the matching language should be shown, fallback languages should be English.

For CI the dialog for creating a notification should allow to add more languages if needed as an optional step.