Feedback form: Changed component type from plugin to other so JS and CSS are no longer part of core

@cfarquharson Note that this also brings about the new .nojs-show and .nojs-hide classes. With nojs-show it hides when JS is enabled (display: none) and shows when JS is disabled (display: block). With .nojs-hide, it only hides when JS is disabled (display: none). This should be documented in the style guide.