Allow selectable QBtn

[paya-cz]

QBtn has the following class hard-coded: non-selectable. I do have a need for a button with selectable text. There doesn't appear to be a simple way to remove this class from the button except using vue directives. Please consider adding a property that would let me remove the non-selectable class.

The use-case is for something akin to table values (or values in text etc) which have a primary function when clicked (copy to clipboard) but should also allow the user to select sections of the website and have the button label be selected together with the surrounding text.