Add API output skin

The API output for help and 'fm' formats will soon have need of
including ResourceLoader modules on an otherwise-bare page. The easiest
way to do this is to use OutputPage, but that requires a skin. So let's
add a skin that outputs a basic page without any navigation elements or
other chrome (that may be added later, but that can wait for Design to
decide they want to design it).

Change-Id: Ifa95fae5acaa3cfbf2ca58a15f8d0c51d84b455a
Merge "Add API output skin"