Add IE8 compatibility

Adds html5.js to allow IE8 to recognize html5 and thus fix major layout problems. 
Adds respond.js to enable media queries in IE8.
Commit de15a83 fixes class and pseudos issues with selectivzr-min.js. No extra CSS needed to make layouts work in ie8.  
Adds option under Global>Advanced to enable IE8 compatibility.

<h3>ISSUES</h3>
Breaks font icons. Dirty fix is to add the style with link before closing the head for ie8 only. 

<h3>Before</h3>
![before](https://f.cloud.github.com/assets/1617798/1113588/c9d7d66a-1a00-11e3-85ca-f32c5027a2ef.png)

<h3>After</h3>
![after](https://f.cloud.github.com/assets/1617798/1113592/d0a42264-1a00-11e3-9b78-7c7d98738dcf.png)

<h3>The Option</h3>
![the option](https://f.cloud.github.com/assets/1617798/1113614/501b86cc-1a01-11e3-806b-2ea8499a8605.png)

<h4>NOTE</h4>
The child theme also has the border-box model implemented, with the exception of the PL Editor toolbox which breaks with border-box.
<pre>
*, *:before, *:after {
-moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box;
 }
 .toolbox-handle, .toolbox-handle:before, .toolbox-handle:after {
 -moz-box-sizing: content-box; -webkit-box-sizing: content-box; box-sizing: content-box;
 }
</pre>