Activate tag-it for multi-select inputs.
Use aker-rails instead of aker.

Aker-Rails includes useful Rails hookups, which we'll probably want,
given that this is a Rails app.
Generalize input field styles.

The tagit plugin generates something that is meant to look like an input
field but does not strucurally resemble one.
Styles for tag-it.

This commit also generalizes the horizontal pause used between inputs
and their labels to the concept of a beat, which I have (loosely)
adopted from theater and film.  I'm sure there's a more typographically
appropriate name for this, but I can't think of it offhand.