Boilerplate: Bootstrap
RSVP: Add form validation and flow service

Start to add the frownies in from previous
years. Add a rsvpFlow service that knows
where we are in the RSVP flow, so we can
do things like next() and forget about it.

Rework the stylesheets so the RSVP flow has
its own style.
RSVP: Add dancer role

Use buttons!