Bower package definition

@camertron

Though `twitter-cldr-js` went from being a set of JS files to being a
gem whose primary goal is to integrate with the Rails assets pipeline, there is
value in defining a Bower package for JS developers who simply want to make
use of CLDR from, e.g., their Node code.

I have no experience defining Bower packages and might have missed something —
it looks like the package manager will simply pull the entire git repo (at least that's
what happened when I tried to test locally). It's not a very big deal anyway, since
developers should ultimately filter and compile the `.js` files when their project is 
deployed. The file was automatically generated by `bower init` and refers to the latest
git tag (2.2.1), which isn't the latest release on rubygems.org (what gives?)

In any case, Bower being a project maintained by Twitter, I think it'd be nice to have
some amount of coordination between their project and this one.