Allow ignoring of audio data tracks on import

[fortes]

#1638 by @jdetrey changed the importer to take data tracks into imports. This adds a configuration option to disable that feature.

I'm proposing adding this since it seems like video tracks still get included sometimes in data-track-list, such as in this release where there is a multimedia track: http://musicbrainz.org/ws/2/release/cbc97377-05f3-4011-a8fa-0aaa1ca9ffd1?inc=artists+artist-credits+recordings+aliases

[sampsyo]

Looks good! My only question is whether this option should be on by default. You probably have the default right already, but it would be worth considering flipping the default too.

[fortes]

@sampsyo I debating setting this to yes until I found the PR that just enabled the feature a few months ago, so I went conservative here in order to avoid breaking people's config.

I'd personally have this as yes by default, but can see the other side of the argument.

Will merge now, I figure we can always change the default in a separate PR.

[sampsyo]

OK, sounds good! I would not object to switching the default to yes—this is a new enough feature that I doubt many people are relying on it. (We probably should have put this behind an option to begin with.)