Js improvements

Fixes #281 and fixes #273

- Adds fastclick
- Move customer js to the bottom of the page
- Moved Modernizr to bottom of page
  - This is not recommended with IE8 support still on the table because of the HTML5 shiv, but we load that conditionally at the top of the page in `oldIE-js.liquid` rather than as a part of Modernizr
- Move comment hash JS helpers to Timber's `shop.js`
- Move login/recover password JS to Timber's `shop.js`

Demo shop for new updates - http://steve-dev.myshopify.com/

@stevebosworth @mpiotrowicz 
can it be re-written so that liquid sets a flag to true that `init` then checks? It's preferable to move all JS to `init` especially if in this scenario causes an awkward second call to `cacheSelectors()`