Override Jenkins CSS for long settings description

Summary:
I think the Jenkins styling that .pane has white-space:nowrap is too
broad. This broadens up my previous CSS override to apply to all
setting-description classes, not just those in a particular .pane
instance.

Test Plan:
I made this change in ~jenkins/userContent/ on jenkins.khanacademy.org
and then in my browser visited (with a hard cache refresh)
http://jenkins.khanacademy.org/job/deploy-staging/112/promotion/ in my
to verify that the long description of the "CLEAN" parameter does indeed
wrap its text and the "Re-execute promotion" button visible without
having to scroll to the right. I didn't have to restart the Jenkins
server because the nginx reverse proxy handles reading from the
userContent/ directory.

Reviewers: tom

Reviewed By: tom

Differential Revision: http://phabricator.khanacademy.org/D3733