updated help

...in/java/com/ardublock/ui/listener/HelpButtonListener.java

...in/webapp/com/ardublock/reference/_seitenformatierung.css

src/main/webapp/com/ardublock/reference/addition.html

src/main/webapp/com/ardublock/reference/arduBlockHelp.png

src/main/webapp/com/ardublock/reference/division.html

src/main/webapp/com/ardublock/reference/help.html

src/main/webapp/com/ardublock/reference/modulo.html

src/main/webapp/com/ardublock/reference/multiplication.html

src/main/webapp/com/ardublock/reference/simHelp.html

src/main/webapp/com/ardublock/reference/subtraction.html