Add `list` field type (available in blueprints) to frontend forms

[hughbris]

My use case is that I am requesting a set of name and date-of-birth pairs, so an Array type field won't suffice.

I've tried to hack this up based on the Admin field (advised by @w00fz a while back), but my JS foo and tooling is pre ES6 and I'm lost.

Currently I've resorted to repeating four pairs of these fields in columns. It's not pretty code or UX.

This seems like an essential in the toolbox for those of us who develop medium to complex public forms regularly.