Bug fixes and performance improvements

Visualizer uses no CPU when inactive

The Visualizer now does not perform any computations or graphical rendering when the player is either paused or stopped. This eliminates unnecessary CPU usage.

#67 - Fixed app icon (menu bar mode)

Thanks to @BillGoldenWater for the bug report!

Window snapping behavior improvement

The way that the separate app windows snap to each other has been improved, eliminating some of the awkward (jerky) snapping behavior when the main window is dragged.

Updated Copyright year in source code and license