Restricted monitoring for very large suites

This makes the CLI monitor and GUI perfectly usable for massive suites (>10K tasks) by only displaying the 'active' task states and disabling the graph view.

It may be possible to make a GUI that can handle massive suites in full, but that's a more difficult problem, and I think this is a nice interim measure at the least.

I made it a command line option because the normal unrestricted display is likely to be unresponsive, so that clicking on a GUI control to switch to the restricted option may not be practical.  However, we could add that later.

@benfitzpatrick - please review.