send_later: Pick time from 'Custom time' link.

This introduces a 'Custom time' link to the bottom of the scheduling
modal's options. Clicking on it pulls up the date picker.

Additionally, clicking on the 'Custom time' link, then clicking
elsewhere to close the time-picker, then subsequently clicking
'Custom time' again reveals the time-picker.

However, repeatedly clicking the 'Custom time' link while the
date-picker is already open will cause the date-picker to redraw
each time.

web/src/popover_menus.js

@@ -910,9 +910,9 @@ export function initialize() {
                                 e.target.click();
                             }
                         });
-                        $send_later_modal.one("click", ".send_later_date_input", (e) => {
+                        $send_later_modal.on("click", ".send_later_custom", (e) => {
                             flatpickr.show_flatpickr(
-                                $(".send_later_date_input")[0],
+                                $(".send_later_custom")[0],
                                 update_scheduled_date_from_modal,
                                 new Date(),
                             );

web/templates/send_later_modal.hbs

@@ -26,6 +26,9 @@
                                 <a id="{{@key}}" class="send_later_tomorrow" tabindex="0">{{this.text}}</a>
                             </li>
                         {{/each}}
+                        <li>
+                            <a class="send_later_custom" tabindex="0">{{t 'Custom time'}}</a>
+                        </li>
                     </ul>
                 </div>
             </main>