#13 feature request: allow closing of main window

I think it would be nicer if StreamRipperX would let the user close the
main window and still continue its operation. This is inline with how
iTunes works. It would make the program feel more like a native mac
program if this was the case. Even better would be some indications on
top of the dock icon that shows what the status is.

Thanks for the great program,

Tyler Riddle