[FR] Syncthing should complain loudly when items fail

[Catfriend1]

Quote from @klement syncthing/syncthing-android#747

Nexus 6P/Android 7.0/Syncthing v0.14.6
I recently hit a permissions issue which stopped my sync - even though SOME items couldn't sync, NO items would be synced. I only noticed this because I changed my pwd database on the PC and needed to use it the next day on mobile and it wasn't synced.
So if there are any items failed - syncthing should complain loudly using a notification instead of silently not doing its job.

[Catfriend1]

This is solved with #381 and the check for the sdwrite permissions on folder creation and the check for the sdcard android permission on app startup. I think all those fixes we made during the last year are enough to notify the user if issues arise. There's also a red text on the UI "not synced" if something went wrong.
@klement : Let's close this unless anyone that had chance to read the ticket within the 3 years it already existed is willing to implement more safe-guards or popup notifications.