Improve envelope greeting

If the user changes the envelope_greeting to "Mr. and Mrs. Doe" and then they mark John Doe as deceased, I believe it won't regenerate the greeting because then "John" won't be in the envelope greeting. That makes sense to me to check for the presence of the first name for the contact name since that usually will indeed have the first name in it, but I guess I'd err on the side of caution and suggest just regenerating the envelope greeting when someone dies, i.e. remove the `c[:envelope_greeting].include?(first_name)`.