Bug 8883: 'opacsmallimage' doesn't work in ccsr theme

This patch makes it possible to customize the CCSR theme using the
opacsmallimage system preference. It also enables the LibraryName
preference for opacsmallimage alt text.

To test, set the opacsmallimage preference and switch to the CCSR
theme. Your custom image should appear. Set the LibraryName preference
and confirm that the alt attribute of the custom logo changes
accordingly.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>

This patch works correctly, although it lacked a description and test
plan, which I have added. I would have used IF instead of UNLESS because
to me that seems more readable, but it's not a deal-breaker.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Merge branch 'bug_8883' into 3.12-master