Fix #467 -- Pluggable email placeholders (#1429)

* Fix #467 -- Pluggable email placeholders

* Previews

* Polishing

* Fix tests

* Add missing doc file

src/pretix/static/pretixcontrol/js/ui/mail.js

@@ -6,6 +6,7 @@ function preview_task_callback(data, jqXHR, status) {
             var target = $('div[for=' + data.item + '][lang=' + m +']');
             if (target.length === 1){
                 target.html(data.msgs[m]);
+                target.find('.placeholder').tooltip();
             }
         }
     }
@@ -32,6 +33,7 @@ function preview_task_error(item) {
 $(function () {
     "use strict";
 
+    $('.mail-preview .placeholder').tooltip();
     $('a[type=preview]').on('click', function () {
         var itemName = $(this).closest('.preview-panel').attr('for');
         if ($('#' + itemName + '_panel').data('ajaxing') || $(this).parent('.active').length !== 0) {
@@ -64,4 +66,4 @@ $(function () {
         );
 
     });
-});
+});

src/pretix/static/pretixcontrol/scss/_forms.scss

@@ -141,6 +141,10 @@ div.mail-preview {
   border: 1px solid #ccc;
   border-top-width: 1px;
   border-radius: 3px;
+
+  .placeholder {
+    background: transparentize($brand-warning, 0.6);
+  }
 }
 
 .mail-preview-group div[lang] {