[options] add an initial theme option page with one option

The one option lets theme users hide the "Got something to add? Find
me on Twitter and Google+" section underneath content. Although it
would still be great to allow configuration of these values, theme
configuation feels like the wrong place to me.

Hopefully they (or, at least Twitter) will be added as user profile
fields soon, then this option can disappear and only appear when
appropriate.

This settings page is based on instructions from:
http://themeshaper.com/2010/06/03/sample-theme-options/