Bug 859537 - Add specific rules for Russian slides

Added specific CSS rules to avoid text being displayed outside of the
background on slide #2 and #14. See
https://bugzilla.mozilla.org/attachment.cgi?id=756382 for screenshots
with this change applied.
Merge pull request #937 from flodolo/bug-859537-fix-mozilla15-ru

Bug 859537 - Add specific CSS rules for Russian slides