Multi-controller support!

It was asked quite a few times if multiple controllers can be watched at the same time, and I heard you~ The polling routine was rewritten to support cycling through multiple controllers, the tray icon switches status display every 5 seconds.
Also, the low battery notification was changed. Before, it used the "old" balloon message system that was common in Windows versions up to 7. Now the "new" toast system introduced with Windows 8 is used. This (probably) means that notifications won't work properly in Windows 7 any more.

IMPORTANT Windows 10 1709 broke the toast notification for this version. Please update to v1.2.0!