check for at least one track before getting artwork
check the artwork preference before doing anything else

This method has nothing to do if artwork is disabled.
initialize all variables
combine artists without a mutable array
bump version to 2.3.1
fix some warnings
remove a call to updateIcon

Not sure how this snuck in.
use the size supported by the current interface
remove unnecassary NSImage methods
try to capture and log errors from Scripting Bridge calls