Add search filter for quickly finding icons

I added a search filter to the icons page, so I can quickly sift through them when I'm looking for something in particular. 

Demo: http://screencast.com/t/MhpzzMjE

I didn't have a way to compile site.css since I can't run a Makefile--sorry for that. I just appended the CSS declarations manually so it would run. But they are in less and will build the next time you compile it.