[fix] simple theme: move engine alerts in case of no results into sidebar

If there were no results but errors in the engines then the error dialogs of the
engines was displayed in the result list.

With the new design errors of the engines should only be displayed in the
sidebar and at the same time duplications of the (template) code will be
avoided.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>