Small control inputs and input groups

[jrubenoff]

Support small inputs for checkbox / radio buttons, and input groups.

See http://dvlcore.dev/forms for examples.

[jrubenoff]

Also, @ajb, if you're curious as to when small inputs should be used, I added a note to the style guide.

[ajb]

Cool, looks good. This still needs help though, even after I fixed the class names:

[jrubenoff]

I wanted to keep the checkbox the same size so that it's not more difficult to press.

[ajb]

OK, you might need to change the line height for proper vertical alignment?

[jrubenoff]

Ahhh, thanks. Done.