Fix Datepickers in Call for Content

Datapickers in Call for Events/Booths/Tracks were broken which made impossible
to create them (as the date is required).

Those are not the only Datepickers broken and a similar solution should work
for the rest as well.

Fixes https://github.com/openSUSE/osem/issues/2349

app/assets/javascripts/osem-datepickers.js

@@ -66,22 +66,19 @@ $(function () {
        format: "YYYY-MM-DD",
    });
 
-   //   end_date_conference >= registration-period-Start_date >= Current_date
-   //   registration-period-Start_date <= registration-period-End_date <= End_date (of conference)
-   $("#registration-period-start-datepicker").datetimepicker({
-       pickTime: false,
-       useCurrent: false,
-       format: "YYYY-MM-DD",
+   // today <= start_registration <= end_registration <= end_conference
+   var end_conference = $('form').data('end-conference');
+
+   $('#registration-period-start-datapicker').datetimepicker({
+       format: 'YYYY-MM-DD',
        minDate : today,
-       maxDate : $("#registration-period-start-datepicker").attr('end_date'),
+       maxDate : end_conference
    });
 
-   $("#registration-period-end-datepicker").datetimepicker({
-       pickTime: false,
-       useCurrent: false,
-       format: "YYYY-MM-DD",
-       minDate: today,
-       maxDate : $("#registration-period-start-datepicker").attr('end_date'),
+   $('#registration-period-end-datapicker').datetimepicker({
+       format: 'YYYY-MM-DD',
+       minDate : today,
+       maxDate : end_conference
    });
 
   $("#conference-start-datepicker").on("dp.change",function (e) {

app/views/admin/cfps/_form.html.haml

@@ -7,15 +7,15 @@
 .row
   .col-md-8
     = semantic_form_for(cfp, url: cfp_form_url(cfp, conference),
-      html: { multipart: true }) do |f|
+      html: { multipart: true,
+              data: { end_conference: conference.end_date.to_s } }) do |f|
       = f.input :cfp_type, as: :hidden
       = f.input :start_date, as: :string,
-        input_html: { id: 'registration-period-start-datepicker',
-          start_date: conference.start_date,
-          end_date: conference.end_date, readonly: 'readonly' }
+        input_html: { class: 'form-control',
+                      id: 'registration-period-start-datapicker' }
       = f.input :end_date, as: :string,
-        input_html: { id: 'registration-period-end-datepicker',
-          readonly: 'readonly' }
+        input_html: { class: 'form-control',
+                      id: 'registration-period-end-datapicker' }
       = f.input :description, hint: markdown_hint,
         input_html: { rows: 2, data: { provide: 'markdown-editable' } }
       - if cfp.cfp_type == 'events'