Expose Flatpak's end-of-life information

A commit in flatpak can be marked end-of-life, as in it is no longer expected to get updates, and with that it can have a custom message or redirect to a new package replacing it. Appcenter should expose this information in the UI in some form.

The basic API docs are here:
- http://flatpak.github.io/flatpak/reference/html/FlatpakTransaction.html#FlatpakTransaction-end-of-lifed

- http://flatpak.github.io/flatpak/reference/html/FlatpakRemoteRef.html#FlatpakRemoteRef--end-of-life