LP1807461 Admin page avoid errors on dialog dismissal

LP1807461 Admin page avoid errors on dialog dismissal

Add support to the base DialogComponent class for passing information to
the caller via the reject handler about whether a dialog was dismissed
via user interface interaction (body click, esc key, cross click, cancel
button) or for some other reason, presumably an error.

Teach the generic admin page to avoid toasting errors when an edit or
create dialog is dismissed via UI.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Dan Wells <dbw2@calvin.edu>