Use links for CMS preview states to allow open in new tab

Important to allow users to send around preview links, open draft versions in
new tabs, or find out which URL to use to preview on mobile phones and other
devices which can't load the CMS preview panel directly.

Removed CSS animations since they complicated the component too much.

Removed input/label setup since its not contained in a form, so has no
relevance as far as server-side state goes.

This does mean there's no longer an indication that only one state can be
active at a given time (which the radio buttons communicated), but that's no
different from e.g. the CMS menu.

Not an API change since the Entwine JS and PHP interfaces stay the same.