Adapt to recent beets core changes

[JOJ0]

• decargs was removed from beets core. I fixed the import and passed args directly. see https://github.com/beetbox/beets/commit/a815305fcd7834da2afe1feac0e786c44d4979b2
• DurationType was moved to a types module. Fixed.

These changes make the plugin functional again. Hope it helps and all the best!