Add a static features mode to the Track Monitor

Add a new "static features only" mode to the Track Monitor. When activated, this mode would conceal all signal aspects with a generic image. It would communicate the locations of signals, but not their states, reflecting the route knowledge that a real train driver would have. It would also hide any switch status indicators. Static mode would be toggled with Shift+F4.

Discussion: http://www.elvastower.com/forums/index.php?/topic/34424-removing-signal-aspects-from-the-track-monitor/