Fix LP 829630, Show in Catalogue not working on Bills screen

Fix LP 829630, Show in Catalogue not working on Bills screen

The page is looking for a messagecatalog XUL element with id
'catStrings', but is not finding it, and so we add it to the relevant
XUL file.

It's odd why it is omitted, because a browse through the repository
doesn't show any changes that would explain the error.

Signed-off-by: James Fournie <jfournie@sitka.bclibraries.ca>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>