add defaul css rules in dedicated stylesheet file

I'm a person who looks more intense to the code instead of a README.md file. So I overlooked the section, where it is explained which styles should be copied to your custom stylesheet file. I didn't get the button's icon displayed and thought, that this might be a bug.

I added a Control.FullScreen.css file, because I think it belongs to this package. I like it to have least possible integration work, and with this change, I just have to include another css file. The extra http request can be easily avoided by: 1) Integrating the css like before, 2) using an css compiler which merges all css files into one.