Use idiomorph and a delay in the booking form

This is specially for the departure date: Firefox triggers a change each
time the user writes something, but since the date may be outside the
allowed range while the user is typing, the form replaces the input with
the “corrected” one.  The idiomorph thing is to keep the focus in the
“same” field, from the point of view of the user.

It still happens if one is slow enough, but i guess people that want to
write instead of picking the date are usually fast typist. Let’s hope.

web/templates/public/booking/fields.gohtml

@@ -21,7 +21,8 @@
         </fieldset>
         {{ with .Dates -}}
             <fieldset class="booking-period"
-                      data-hx-get="/{{ currentLocale }}/booking" data-hx-trigger="change"
+                      data-hx-get="/{{ currentLocale }}/booking"
+                      data-hx-trigger="change delay:1000ms"
             >
                 <legend>{{( pgettext "Booking Period" "title" )}}</legend>
                 {{ with .ArrivalDate -}}

web/templates/public/booking/page.gohtml

@@ -7,6 +7,10 @@
     {{( pgettext "Booking" "title" )}}
 {{- end }}
 
+{{ define "head" -}}
+    <script src="/static/idiomorph-ext@0.3.0.min.js"></script>
+{{- end }}
+
 {{ define "content" -}}
     {{- /*gotype: dev.tandem.ws/tandem/camper/pkg/booking.publicPage*/ -}}
     <h2>{{ template "title" . }}</h2>
@@ -21,6 +25,8 @@
         </div>
     {{- end }}
     <form id="booking" action="/{{ currentLocale }}/booking" method="post"
+          data-hx-ext="morph"
+          data-hx-swap="morph:innerHTML"
           data-hx-include="this"
           data-hx-target="this"
           data-hx-replace-url="true"