Added tests for pages via Mink

This tests the whole library and pages without mocking via Mink and the Selenium Driver.
Just now only basic but we can improve them and add more later.
I see. You're using `NodeElement` methods to make it work.

>  but I fear that using RadioButton as single element might not work as expected, cause getValue will always return the value of a selected radio button, if none is selected in that group NULL is returned.

Not to worry. Look at `getValue` implementation of any driver. There the other radio buttons with same `name` attribute are found and value of selected one is returned.