Honeypot captchas + flash message css fix

1. I added the [honeypot-captcha gem](https://github.com/curtis/honeypot-captcha) and used it on the prediction form and comment form to prevent spam. Using the terms in [this explanation of honeypots](http://nedbatchelder.com/text/stopbots.html) the gem should protect against the "form-filling bots", but not "playback bots." Since the spammers don't seem to actually be getting any URLs into their comments, I doubt they're playback bots.

2. I made a fix to a CSS bug where multiple flash messages would overlap.

3. I also fixed some typos in the "INSTALL" instructions.