Implement error page template

tpl/error.tpl

+{extends file='page.tpl'}
+
+{block name=main}
+    <div class="alert alert-warning">
+        <h2>{$error}</h2>
+        <p>{_('Back to the homepage of')} <a href="{$SERVER_URL}">{$APPLICATION_NAME}</a></p>
+    </div>
+{/block}