Added responsive nav and configurable js options

Added responsive nav from:
http://www.smashingmagazine.com/2013/04/09/responsive-nav-a-simple-javas
cript-plugin-for-responsive-navigation/)

Also, moved all scripts to _scripts.html partial so here is only one
place to manage script imports, and made all supported, scriptable
items configurable from config.js (meaning all SCSS and JS are
configurable largely from just two files).