Delete MythUINotificationCenter when quitting applications.

Also add some safeguard, just in case some messages are received while we're currently deleting the notification center
Handle PNG coverarts

Make it so that we should handle more type should they ever be sent by iTunes
Implement progress bar in UIMythNotificationScreen

Create new MythNotification: Playback that contains playback progress and Media that includes an image and playback progress.
Only display UI elements that are actually in use.

Redefine MythNotification::Update type: only fields changed are actually refreshed; this prevent redrawing all fields all the time
Use new progress bar in MythUINotificationCenter to display duration and position of song currently playing
Merge remote-tracking branch 'upstream/master'
Properly handle fd number 0 in signal manager

Visual analysis (IEAEYEBALL) detected that the
check for the file descriptor value should be
"fd >= 0" and not just "fd > 0".  While a fd of
zero is commonly stdin, do the right check just
in case.

The CLOSE macro properly performs the check
for greater than or equal to zero.  This
patch just does the same thing.

Signed-off-by: Gary Buhrmaster <gary.buhrmaster@gmail.com>