Application icon [resolves #16]

Add a new application icon (I'm not an artist!) based on
markdown-mark (https://github.com/dcurtis/markdown-mark) and
kate application icon from oxygen icons (http://www.oxygen-icons.org/).
Another try to hide syntax help on application start
README.md and images

* simplify README.md again
* added link to heise.de
* removed now unused images