Polling interval field CSS update

As described in ticket: https://issues.apache.org/jira/browse/COUCHDB-2371

I also changed the slider event from onChange to onInput which continually fires when the user drags the slider. It results in more code being called but it has a much better feel, I think: i.e. the # seconds updates during dragging, not just afterwards. This was probably what was originally intended: Chrome changed the onChange event behaviour a few months back to only fire after the drag is completed.
this looks a bit weird as it mixes tabs and spaces (see: https://github.com/benkeen/couchdb-fauxton/blob/2371-polling-interval-slider-css-fix/app/addons/activetasks/templates/tabs.html)