Better Fullscreen detection

Now allows you to add a fullscreen program to a whitelist, such as Remote Desktop, or a non-demanding game by right-clicking on the tray icon and selecting the Ignore option. Only presents the last detected fullscreen program.
This needs more testing, but so far it works well.

Also averages CPU usage over a longer period to help prevent quickly starting/stopping mining when short bursts of high CPU utilization occur, such as launching a program or starting a video.