Bug 23261: Add notice for login/registering to RBdigital results

Bug 23261: Add notice for login/registering to RBdigital results

To test:
 1 - You will need a valid library RBDigital account
 2 - Fill in the RecordedBooks system preferences
 3 - Open the catalog, perform a search with RBDigtal resuls, 'love' often works
 4 - Click to the results
 5 - Note if not logged you don't see availability
 6 - Log in with a patron with no email, note you do not see any notice that you must register your email with RBDigital
 7 - Apply patch
 8 - Reload results, you now see a notice to register with rbdigital, do so unless you already have an account
 9 - Add your associated email to the koha account
10 - Reload results, note you see availability
11 - Log out, reload results
12 - Note you see a promp to login to see availability

Signed-off-by: Jessica Zairo <jzairo@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>