Add jQuery UI library

Author: adamhb123

_includes/head.html

@@ -24,6 +24,7 @@
 
     <!-- Javascript libraries -->
     <script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
+    <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.min.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js"></script>
     <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
     <script src="https://cdnjs.cloudflare.com/ajax/libs/slick-carousel/1.9.0/slick.min.js"></script>