Remove Coverity warnings...

Those returned values do not need to be checked.
Don't return early when deleting a client

Done so the log contains more information
Add MythUINotificationCenter

Preliminary Notification Center manager. Will allow for an application to send informative message that will be queued and displayed to the screen in a permanent or temporary fashion.

For the time being, only handle a permanent position and uses the music miniplayer theme for ease.
First client will be the AirTunes (AirPlay) server that will display artwork and information about the song being played
Make AirTunes (RAOP) server use new MythUINotificationCenter

Will display artwork and song being played information (artist, album name, title and file format)