Force checkboxes

[Aybee]

Sometimes you have 1 answer out of 3 set to true, but you do not want to give a hint that only one answer is true. But with radios you immediately see that only one answer is true and user can only select one input. For this situation we need an option 'force_checkbox'.

Short:

1. answer = true
2. answer = false
3. answer = false

results always in radios.
We need an option to force checkboxes here.