New POJOs to implement backup and restore functions
Fix menu items order.
Fix application theme.
Update overflow icon color to match
File is now copied on internal storage in private mode.
Restore menu item is only displayed if there is at least one backup.
Display a dialog to pick a backup
Add missing resources
Fix xxhdpi resource
Preferences can be restored and deleted
Merge pull request #6 from SimonMarquis/backup_and_restore

Backup and restore