Fixing behaviour of QBooleanElement to be consistent

Ok, this one is ok.
As stated in #200 this pull request is for making a consistent behaviour for QBooleanElement so using either way of displaying value results in the same handlers being called.

To do so, selection handler is disabled (as I don't see a point on handle the selection on a QBooleanElement) and value changes handler uses controllerAction or onSelected as it was done previously only for switch style QBooleanElements.