added suppoer for gnome-keyring
RepoPass for encrypted library is stored in gnome-keyring instead of the sqlite3 database
added fallback for old style repo password read
If the gnome-keyring support is enabled, the password search in this order
 - gnome-keyring
 - if not found,  sqllite3 database

If the libarray is removed from syncing the password is removed from both
 - sqlite3 database
 - gnome-keyring

In case of the upgrade, the RepoPassword will not be automiticaly migrated to
the gnome-keyring. User needs to unsync and sync the library again.