Bug 3383 - Item due reminder digests - cannot display title information

Bug 3383 - Item due reminder digests - cannot display title information

Adds the ability to use branches.* fields in digest notices and
have them be parsed correctly. Also adds a warning to the notices
editor for digests.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
I like the idea to show a warning, but I would perhaps move
it under the message body label to be more obvious.

Patch works nicely, branch data of my user's home library
is displayed in the notice.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>