Seafile as a backup location

[chirayudesai]

It supports SAF, shows up in the Files app, can create files inside that.

It has FLAG_SUPPORTS_IS_CHILD - https://github.com/haiwen/seadroid/blob/5a0710c1d8fc4a57c26dfbc9df201b96c903bbd6/app/src/main/java/com/seafile/seadroid2/provider/SeafileProvider.java#L650 - needed for https://developer.android.com/reference/android/content/Intent#ACTION_OPEN_DOCUMENT_TREE

[chirayudesai]

This could be a good addition, it's open source.

https://www.seafile.com/en/home/

https://f-droid.org/en/packages/com.seafile.seadroid2/

[jtagcat]

Duplicate of #84