Bug 7599 - [SIGNED-OFF] Cart JavaScript contains untranslatable English strings

Bug 7599 - [SIGNED-OFF] Cart JavaScript contains untranslatable English strings

To simplify the sentence structure for better translation flexibility
the message now reads:

"Item in your cart: " + number

Fixed in both OPAC and staff client, although I'm not sure
the message is actually triggered in the staff client.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Strings become translatable

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>