fix bug 1012965 - Date picker looks broken in chrome

I implemented a check that sets the boolean `dateInputSupported` on `window`.
In case date inputs are supported by the browser, jQuery UI is not used. This is especially nice for mobile.
However, style should still be somewhat adjusted to accomodate for UI bits Chrome adds (date doesn't fit in the box anymore).
You could move this to a function in `fjord/base/static/js/fjord_utils.js` and call it here and the other places.