conflictying jquery versions are appiled to the page,
the datepicker adds jquery in the head of the page:
<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
you are adding it again near the end of the page:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
jquery can only be applied to the page once.