Add about sections

* Add about SaferNYC and about the data sections
* Add links to view about sections as pop-ups
* Add JavaScript to enable pop-ups
* Style links and about sections
* Make HTML, JS code improvements
I think the screen reader will avoid things that are display none'd consider using aria labels

http://www.paciellogroup.com/blog/2012/05/html5-accessibility-chops-hidden-and-aria-hidden/