javascript libraries: CDN and local hosting

[espinielli]

It looks like a good/safe approach for external javascript libraries is to:

1. use CDN
2. have a fallback reference to our web host

A code example is:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
<script>!window.jQuery && document.write(unescape('%3Cscript src="includes/js/libs/jquery-1.6.1.min.js"%3E%3C/script%3E'))</script>

This should be done in _head.html (and cleanup all other places where we load things).

Also check Modernizr: we have (an old-ish version of) it but I am not sure how/if it is used.

NOTE/RISK: how to safely keep aligned versions numbers of referenced and locally hosted javascript libraries...maybe we need a Rake task to check for this...or have a YAML config file...