We use the application ID now to ensure uniqueness if the same folder is selected
between different app versions/forks. This will make more sense once storage
settings are unified to a single location.
Also changes the file extension while we're at it so people stop accidentally
ungzipping it.
(cherry picked from commit cc018cee182f880ebfe07e45809a98d0f6d73220)
# Conflicts:
# app/src/main/java/eu/kanade/tachiyomi/data/backup/models/Backup.kt
12774c54ee