Adds a render_icon helper spec.
Prefix all icon font classes.

We use the icon font classes inside of the menubar stylesheets.
But because we are in the website's domain, we accidentally override icon classes of the website.
This commit fixes this.
Adds more style resets to menubar buttons.
Merge pull request #526 from magiclabs/2.9/namespace-icon-classes

(2.9-stable) Prefix icon font css classes.