Add SoundCloud queuing to v3

[gjtorikian]

This adds in the ability to queue SoundCloud URLs. SoundCloud support was added to MPD sometime at or around 0.17.x, along with a lot of other goodies. For that reason, I'm pulling out the Holman Gist, and properly brew installing the official formula.

There are a few quirks to queuing that I think are attributed to the underlying ruby-mpd library. And, of course, additional quirks because most of this code assumes an actual file path. Rather than use TagLib, we'll call out to the SoundCloud API to fetch information. I could add a couple of new database tables to minimize the calls to support this, I guess.

I don't know who's interested in the ping. @holman @thedaniel @maddox @dreww seem like good candidates. Happy to talk offline for the rationale, e.t.c.

[holman]

I think we should really think about what Play is going to be at the office (if at all) before tossing more code in here. It already feels pretty bulky code-wise, and if we're not going to actively use it I'm a little skeptical of adding more code directly to the project.

[gjtorikian]

I think we should really think about what Play is going to be at the office (if at all) before tossing more code in here.

Fair enough. I'm going off the grid for two weeks, I'll try to catch you in mid-March.