Setup for Rack Attack

# What's New?

 A few days ago, @digital-dreamer setup the Rack::Attack gem for us, but left out the config options for us to setup. I have the security settings as follows:

 * Throttle users that sustain 1 req / second over a period of 5 minutes (probably just bots or poorly written scrapers)
 * Throttle requests to /sign_in to a max of 5 attempts in 20 seconds (prevent brute force password attacks)

# What Changed?

 * Manually merged in @digital-dreamer 's stuff because I let it sit for so long there was a merge conflict (sorry).
 * Setup configurations noted above.