Add honeypot to stop spam submissions #166

We've had one spam submission so far. This may not stop every bot, but has the
ability to stop some.
I think ideally we should have an Onboarding model (not database backed) that
has all the organization fields and also the honeypot field. A couple of things
in the controller hint at wanting that (adding address/subscription/user
defaults, separate params for the honeypot, manual validation, etc). This still
felt like the best, simple system for now.

I happened to be up in the middle of the night running tests, and I found this
spec that failed. It set up a recurring event at 12pm and then looked for
occurrences in a two week range. But since I'm running this at like 1am, the
time range didn't quite get to the second event in the series.
Basing the time range from the event `starts_at` should make it work at any time
of day.