Bug 893144 - /newsletter/existing/ styling

The styling sheet on /newsletter/existing ws messed up - the
descriptions were all bolded and the newsletter titles were small.

Reverted styling of the TH part of the table to what it was in an
earlier version of newsletter.less. No way to tell what happened
to it due to rebasing on the original branch.
Merge pull request #1072 from dpoirier/bug-893144-newsletter-existing-styling

Bug 893144 - /newsletter/existing/ styling