now can hover over album art to show its file size

Added kilobyte.size.in.bytes setting to help with calculating album art
file size.
Moved createScaledImageIcon() and determineImageScale() into their own
class.
1200x1200 album art downloaded from iTunes is now scaled to 600x600 in
the program window.
Fixed previous album art not being cleared from screen when trying to
load a new album with no album art results from iTunes.