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
* Add and make use of Sass variables
Merge pull request #14 from HayleyCAnderson/add-words

Add about sections

* Add about sections with popup capability
* Make improvements to JS, HTML, Sass