mu4e: switch to contexts

lisp/init-mu4e.el

            :match-func (lambda (msg)
                          (when msg
                            (mu4e-message-contact-field-matches msg
-                                                               :to "aliced@home.example.com")))
+                                                               '(:to :from :cc :bcc)
+                                                               ".*@home.example.com")))
            :vars '( ( user-mail-address	    . "aliced@home.example.com"  )
                     ( user-full-name	    . "ßingen" )
                     ( mu4e-compose-signature . nil)))