Implementation of the "Custom Tags" Feature

[Nikolaj Hald Nielsen]

I have been thinking about this feature lately as I think it is
something we really need, and I wanted to add a few of my own
comments.

First of all I agree that the feature should definitely be called
"Labels" and not "Tags"

Secondly, about linking to the urls table... this makes sense fro an
implementation standpoint, but it also limits labels to tracks in the
local collection. The way ratings currently works, they can be applied
to pretty much anything, and I think it would be cool if it was
possible to add labels to streams, tracks from services and whatnot as
well.

... just my 2 cents.

- Nikolaj