ADMIN - Don't allow Member function for contact older than association age limit

Update membership function logic to prevent adding the function "Member" on the profile of an individual who is older than the association's age limit (i.e., 41 years for Round Table Germany - different for other clubs and associations).

The restriction logic takes into account the end date of the function being added: If an end date prior to the current date is added, the logic allows the function to be added to the profile.

Answer to Glenn's comment: The feature you are referring to does not allow for the selection of the "Member" function. This check is an important feature to prevent club admins from reinstating their regular former members to full members manually. A practice that is used regularely and not aligned with our statutes.