Improvements in the front-end design

We moved the main menu in a top bar (which now frees more space and allows the administrator to add more custom pages if necessary) and the logo to the bottom, allowing to add now larger website logos. Also we created a new banner zone to the right of the logo (except the previously existing ones in the site column, top and bottom of the pages), which can be used to make announcements on the site or to add advertisements like Google AdSense or similar.