Fix the tray window on Win platform.

[yongli-abc]

The tray window's bounds calculation is too rigid and can't adapt to win platform.
Need to generalise it a bit in order to work on win and perhaps linux.

Currently on MacOS it's displayed below the menu bar.
On win it's much trickier as it might need to be above the task bar / below the task bar / right to the task bar / left to the task bar.... Need to think how to best achieve this...