This change greatly reduces the chance that a backup is not performed
when a new photo/video is made.
Instead of combining the change trigger and additonal constraints (wifi
or charging) into a single worker, these aspects are now separated.
Thus, it is now reliably possible to take pictures while the wifi
constraint is not satisfied and upload them hours/days later once
connected to wifi without taking a new photo.
As a positive side effect, this simplifies the error/retry handling
by directly leveraging Android's WorkManager without workarounds.
The separation also allows to notify the currently running BackupWorker
that new assets were added while backing up other assets to also upload
those newly added assets.
Further, a new tiny service checks if the app is killed, to reschedule
the content change worker and allow to detect the first new photo.
Bonus: The home screen now shows backup as enabled if background backup
is active.
* use separate worker/task for listening on changed/added assets
* use separate worker/task for performing the backup
* content observer worker enqueues backup worker on each new asset
* wifi/charging constraints only apply to backup worker
* backupworker is notified of assets added while running to re-run
* new service to catch app being killed to workaround WorkManager issue
* show notifications on background backup errors
* settings page to configure (background backup error) notifications
* persist time since failed background backup
* fix darkmode slider color
* properly done background backup service
* new concurrency/locking management with heartbeat
fix communication erros with Kotlin plugin on start/stop service methods
better error handling for BackgroundService public methods
Add default notification message when service is running
* configurable WiFi & charging requirement for service
* use translations in background service
