Bug 15394 - Tidy up error messages in OPAC lists

Bug 15394 - Tidy up error messages in OPAC lists

To test:

Create a list in the OPAC, observe the message
Create another list in the OPAC with the same name, observe the message
Delete a list, observe the message

Check the patch itself, look for typos.

Signed-off-by: Aleisha <aleishaamohia@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com
(cherry picked from commit e7e1da85a5f6d770c559aa24964d61486a3c9ccb)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>