Bug 2486: Show user comments in staff interface

Bug 2486: Show user comments in staff interface

This patch the staff interface's bibliographic detail page, adding a tab
that shows comments submitted by users from the OPAC.

To test, apply the patch and restart services.

- If necessary, enable the "OPACComments" system preference and submit
  some comments in the OPAC.
- In the staff interface, locate the title you submitted comments on.
  - The bibliographic detail page should show a "Comments" tab with a
    count of the number of all comments (approved and unapproved).

Sponsored-By: Athens County Public Libraries
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Laura_Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>