CMS-4095 New Input Types - Improved DateTime design

Contains CMS-4036 Input Type Date - Show calendar icon within the input
Fixed bug with arrows in Date and Time content.
Moved button to the input field and updated it's styles.
Added basic functionality for a single-input date-time-picker.
Merge pull request #947 from enonic/CMS-4095

CMS-4095 New Input Types - Improved DateTime design