Automagically save aTV settings.

Save the settings when the user leaves the settings menu. No need to
safely shut down PlexConnect for the settings to be saved.
Separate out change fanart menus.

Adding the fanart to the change poster menus causes the aTV to load
tomany images and can sometimes cause a crash :(
Rename 'Artwork' to 'Poster' / 'Fanart'
Respond to the aTV when requesting to save settings.
Keep Baa happy ;)
Merge pull request #1 from iBaa/master

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