Filter out Markdown and PIL.Image log entries.
Filter out Markdown and PIL.Image log entries.

Python-Markdown and PIL.Image are very noisy and tend to clutter up the
log files. This change makes use of the new log blacklist setting to
filter out entries for these two modules.

Testing Done:
Viewed the review request page. I no longer saw any log entries for these
modules.

Reviewed at https://reviews.reviewboard.org/r/9180/

reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard