[FEATURE] support backup with Seedvault

[AuqW9cQ]

Is your feature request related to a problem? Please describe.
Trying to backup my apps with seedfault, but AFWall+ does not allow data backup.

Describe the solution you'd like
support backup with Seedvault

Additional context
https://github.com/seedvault-app/seedvault

[Jack Pearson]

This requires just a change in the manifest

afwall/app/src/main/AndroidManifest.xml

Line 70 in 733db4b

 android:allowBackup="false" 

android:allowBackup=true