Refactoring "Date" field in commonProps

As discussed in a CCT1 discussion a couple weeks ago, the "date" field of the common Properties would benefit from a refactoring. @karl-uwe.stucky had a suggestion to encourage more details on dates which I can not recall right now. But as of now being limited to three option for dates or having to allow a very non-informative "other" (as we agreed to disalow in !24 (merged)), is not ideal.