Use vendor prefixes to reset box-sizing.

Firefox and older webkit doesn't understand "box-sizing: content-box", but do have vendor prefixes for it.

Bootstrap >= 3 sets the box-sizing to border-box using vendor prefixes and messes up the tabs layout, forcing us to use
them to reset it.  First reported in #32.

Author: nathanstitt

public/stylesheets/DV/components/reset.css

@@ -23,5 +23,7 @@
 }
 
 .DV-docViewer * {
-  box-sizing: content-box;
+  -webkit-box-sizing: content-box;
+     -moz-box-sizing: content-box;
+          box-sizing: content-box;
 }