Allow dynamic change of disabled state in radiolist element

[fnk]

The scenario is that i want do enable/disable a radiolist depending on the state of another form element/property.

[eugef]

@fnk thanks for your PR.
Could you also add a test that proves your change works as expected.

[fnk]

I will conjure a test over the weekend!

[ckosloski]

@fnk do you need any help with your test?

[fnk]

@ckosloski sorry for the late reply. i am currently moving home, hope to get back to you by the end of the week.

[ckosloski]

@fnk do you need any help with creating the tests?