PropsForm.Select transforms booleans into strings

[Alex Canessa]

Passing a boolean as an option resolves into:

{
  [propertyName]: "true" | "false"
}

It would be nice to have it translate into boolean when "true" or "false".

Alternatively, a solution could be to have a PropsForm.Checkbox.

[John Otander]

Great idea, Props.Checkbox added in #202.