Rename ckeditorComponent.disabled to ...readOnly

[engineering-this]

According to specs:
disabled This Boolean attribute indicates that the user cannot interact with the control. If this attribute is not specified, the control inherits its setting from the containing element, for example if there is no containing element when the disabled attribute is set, the control is enabled.
readonly This Boolean attribute indicates that the user cannot modify the value of the control. Unlike the disabled attribute, the readonly attribute does not prevent the user from clicking or selecting in the control. The value of a read-only control is still submitted with the form.

CKEDITOR doesn't support disabled state, so we shouldn't use disabled as alias for read only, because this might be misleading.

[engineering-this]

Closed by #1