progress/resume for item imports
progress/resume for item imports

In this implementation, progress is only saved at the directory granularity,
just like with album imports. This is the only easy way to make the progress
stuff interoperable between the two styles of import. With duplicate detection
in place, this is not such a big deal.

google-code-export/beets,google-code-export/beets,google-code-export/beets