Styling for kt.DateInput

[petrsloup]

We now have kt.DateInput component, which can be used to decorate input[type=date] when native support is now available (klokantech/javascript@e301460):

http://klokantech.github.io/javascript/
(Chrome uses native control, in Firefox goog.ui.InputDatePicker instance is created by calling kt.DateInput.decorateAll('yyyy-MM-dd');)

Minor style fixes are needed for the native version (misaligned arrows?) and complete styling for the javascript version.

Original Closure Library styling for this control:
https://google.github.io/closure-library/source/closure/goog/css/datepicker.css
https://google.github.io/closure-library/source/closure/goog/css/inputdatepicker.css