dialog_widget: Add support for rendering a single footer button.

static/js/dialog_widget.js

@@ -79,6 +79,7 @@ export function launch(conf) {
     // * focus_submit_on_open: Whether to focus submit button on open.
     // * help_link: A help link in the heading area.
     // * id: Custom id to the container element to modify styles.
+    // * single_footer_button: If true, don't include the "Cancel" button.
 
     for (const f of mandatory_fields) {
         if (conf[f] === undefined) {
@@ -99,6 +100,7 @@ export function launch(conf) {
         html_submit_button,
         html_body: conf.html_body,
         id: conf.id,
+        single_footer_button: conf.single_footer_button,
     });
     const dialog = $(html);
     $("body").append(dialog);

static/templates/dialog_widget.hbs

@@ -15,8 +15,10 @@
                 {{{ html_body }}}
             </main>
             <footer class="modal__footer">
+                {{#unless single_footer_button}}
                 <button class="modal__btn dialog_cancel_button" aria-label="{{t 'Close this dialog window' }}" data-micromodal-close>{{t "Cancel" }}</button>
-                <button class="modal__btn dialog_submit_button">
+                {{/unless}}
+                <button class="modal__btn dialog_submit_button"{{#if single_footer_button}} aria-label="{{t 'Close this dialog window' }}" data-micromodal-close{{/if}}>
                     <span>{{{ html_submit_button }}}</span>
                     <div class="modal__spinner"></div>
                 </button>