Switch from Typekit to Google Web Fonts.

I picked a font in Google Web Fonts that looks most like the klavika-web
from Typekit.  Only a designer will note the difference.

The whole Typekit experience kind of sucked:

- The site was down from time-to-time.
- The font was only available for sencha.com, so anybody generating
  their own docs with JSDuck would not get the nice fonts.  Also the
  docs withing ExtJS download didn't have the nice font.  etc.
- Recently the font also stopped working from localhost.
- The JavaScript for adding this *one* font was needlessly big, with
  Google Web Fonts it's just one <link> element.