MythNews: improve media:content parsing in rss feeds

* use the medium or type attributes to determine whether the content is an
  image or video. Previously we ignored the type and ended up trying to play
  an image.

* if we haven't found any thumbnail image then use any images found in the
  media:content as the thumbnail. Fixes #11161.

* parse all the media:content items not just the first one we find.
(cherry picked from commit 7d9c51eb75ae37f39a57eb969c0ad7e532738e8a)
update mythtranscode to work with ac3 with newer ffmpeg

ffmpeg has moved the duration/size of the audio frame to another place, so look
there

links used to figure it out how to move forward
http://ffmpeg.org/trac/ffmpeg/ticket/1240
http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=364c71c80e9124a2624e3bfeb8e84c5cddeda222
http://code.mythtv.org/trac/ticket/2077#comment:42

thanks to Nicolas Pöhlmann for finding the commit that broke it

Refs: #2077
(cherry picked from commit a9b906528)
add NULL check missed in [a9b90652]

found by Jim Stichnoth

Refs #2077
(cherry picked from commit f04a8e42b)
mythmusic: Save playlists to DB when changed not at frontend exit

This changes things so any changes to playlists are saved to the database
immediately rather than cached and saved when the frontend exits.

This fixes a problem were you could lose edits to a playlist if the FE is not
shutdown cleanly like when using the idle timer to shutdown or if you shutdown
the computer from the FE exit menu.
(cherry picked from commit 70143c30dfb67812ecd6cb29e66a10353579054f)

Fixes #11228
Updated MythFrontend English GB translation
from Nick Morrott

Thank you Nick!

Refs #11522

Signed-off-by: Nicolas Riendeau <nriendeau@mythtv.org>
mythnews: fix debugging in NewsSite::parseRSS()
(cherry picked from commit f17a6fd24bab751f00b361249b7d2129108e335d)