Spider data sources for album/track data

[treyhunner]

Information on albums and songs would allow us to weed out "fake" Creative Commons artists that don't actually have any music.

This might also allow us to eventually list the CC licences associated with each artist. There is a demand for this (see this Reddit thread looking for non-NC music).

[macro1]

There may be false negatives... Brad Sucks lists his stuff as "all rights reserved" on Bandcamp, and CC on ccMixter.

[treyhunner]

@macro1 that's a true negative because that means we won't want to link to his Bandcamp page if there is no CC music there.

[macro1]

Bandcamp is now in place, we need something similar for the other sources. Even if the data is available via API, we should take advantage of the task queue to keep the searching quick, and create tasks similar to the scraper that checks the various API's.

[macro1]

A function for retrieving track data from FMA has also been added. Currently runs manually.