title: Contact form 7 Datepicker, date range between 2 dates
body: <p>I would like to have two date field in my Wordpress contact form 7. A start-date and an end-date. The fields will be datepickers from the "Contact Form 7 Datepicker" plugin. 
  When visitor has selected a start-date he should only be able to select an end date that is 4 days later then the start-date. </p>
  
  <p>How can I achieve this by only using the "contact form 7" form creator?</p>