Adjust colors of overview calendar + datepicker

* refs #17460
Fix filling of start date and end date in app form

* Add accidentally removed logic to fill the
  application form's start date and end date with
  dates that have been selected in the overview
  calendar.

* refs #17460
Add check to overview calendar if date is selectable

* If clicking on a selectable day in overview calendar
  a redirect to application for leave form occurs.

* If clicking on a not selectable day in overview
  calendar nothing happens.

* refs #17460
Show holiday on half work days (like 24.12.) in calendar

* If someone has holiday on a half work day, like 24.12.
  or 31.12., the half of the day has the color for public
  holiday and the other half has the color for the
  personal holiday - in overview calendar and datepickers.

* refs #17104