#3063, Radios / Checkboxes als Buttons (Bootstrap)

Implemented for Radios. Checkbox is still open.

Index.rst, AbstractBuildForm.php, BuildFormBootstrap.php, Constants.php: split buildRadio() in constructRadioPlain() and constructRadioButton. After several tries to make a base function for both construct variants, CR decided that the code is much more easier to read with to complete separate layout functions.

AbstractBuildForm.php: Notes of input elements as well as the text of a 'Note' FormElement are now wrapped in the class 'qfq-note' - this aligns the text to the label baseline.