Format classnames with classnames

[prestonp]

@jculvey suggested using https://github.com/JedWatson/classnames to format component classnames.

I'd be happy to add it and update any modules that might need this utility

[wyuenho]

This could be folded into #33

[wyuenho]

One thing that come up in a recent internal code review is, the classnames library doesn't have good support for prefix, that alone will render 90% of the library's functionality useless. Might have to build a wrapper component to support that.

[tajo]

Closing this since we are switching to Fela.