Let resolve API call accept a URL

[jwheare]

If we're resolving from an XSPF or podcast, there should be a way to seed playdar with any URLs included in the XSPF. This will then be returned in the results with the source as the domain, a perfect score, but maybe a lower pref than locally resolved tracks.

[jwheare]

Playdar.js is sending URLs now
http://github.com/jwheare/www.playdar.org/commit/659083d98cde1b40e25e4a28b081a841114ece26