ReadOnly attribute is not passed to the checkbox input

[berdyshev]

I'm submitting a ... (check one with "x")

[x] bug report
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://forum.primefaces.org/viewforum.php?f=57

Current behavior
I have this error, however I've passed the readOnly prop into the Checkbox component:
Warning: Failed prop type: You provided a `checked` prop to a form field without an `onChange` handler. This will render a read-only field. If the field should be mutable use `defaultChecked`. Otherwise, set either `onChange` or `readOnly`.

Another error I'm experiencing is:
Warning: Failed prop type: The prop `onChange` is marked as required in `Checkbox`, but its value is `null`.

The existence of the onChange prop is checked here so no need to mark onChange prop as required in order to be able the make readonly checkboxes.

Expected behavior
Be able to make readonly checkboxes.

• React version:
  16.3

• PrimeReact version:
  1.5.1

• Browser: all

• Language: ES6/7

[RobiFerentz]

This is also a problem when using the SelectButton.

[berdyshev]

this commit is only fixes the second error, but not the first one — main.

[mertsincan]

Added readOnly attribute to Checkbox component.

<Checkbox readOnly={true} ...></Checkbox>

First error's already been fixed; #399

[mertsincan]

@RobiFerentz, could you please create a new issue on github?

[RobiFerentz]

@mertsincan See #401