Add splash screen, fixes #215.
Bump version (2.6.1).
Fix unique visitor tracking in GA, fixes #218.

Now using the cookies correctly, based on http://www.tutkiun.com/2011/04/a-google-analytics-cookie-explained.html

It's hard to test the events because they don't show up in real time, but I hacked
it up to use page views instead of events and was able to confirm new vs. returning
visitors.