Improve search field caption for screen readers

Use unicode ellipsis instead of dots to not confuse screen readers. Screen readers shouldn't read 'dot dot dot' when focusing the search button.

application/views/scripts/layout/menu.phtml

@@ -5,7 +5,7 @@ use Icinga\Web\Widget\SearchDashboard;
 <? if (SearchDashboard::search('dummy')->getPane('search')->hasDashlets()): ?>
     <form action="<?= $this->href('search') ?>" method="get" role="search">
         <input
-            type="text" name="q" id="search" class="search" placeholder="<?= $this->translate('Search...') ?>"
+            type="text" name="q" id="search" class="search" placeholder="<?= $this->translate('Search') ?> &hellip;"
             autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"
         />
     </form>