Allow various Gnus and Message address variables to be functions

Allow various Gnus and Message address variables to be functions

* doc/misc/gnus.texi (To From Newsgroups):
gnus-ignored-from-addresses can be a function.

* doc/misc/message.texi (Wide Reply):
message-dont-reply-to-names can be a function.

* lisp/gnus/gnus-icalendar.el (gnus-icalendar-identities):
message-alternative-emails can be a function.

* lisp/gnus/gnus-notifications.el (gnus-notifications):
message-alternative-emails can be a function (bug#22315).

* lisp/gnus/gnus-sum.el
(gnus-summary-from-or-to-or-newsgroups):
gnus-ignored-from-addresses can be a function (bug#22315).