Move browsehappy comment to lt IE9

Since we're using jQuery 2+, it makes sense to warn IE8 users that
their browser isn't supported.
Switched back to google cdn for jQuery

The google CDN seems to be faster and have a little better market
penetration, thus increasing the chances of the user having it cached
already.
Add piwik tracking code example

Instead of HTML5BP's inline Google Analytics script, I've added Piwik's
tracking script (with an example domain). Piwik provides the same
functionality, is just as easy, open source and more privacy friendly
than Google Analytics.
Moved HTML5BP's css name to comments inside build block

Since we're using a build step, the js and css can just be given
generic names. The comments inside the build blocks will tell users
which is which (these are still taken from HTML5BP).