Fixed some bugs in the simulator.

The screen targets were not always redrawn. This is supposed to fix
that. There should be no incidence on the scripts.
Added pictures to Qinetiq task_nullify.dex.
Memory leak and other info.
Make sure the mass is good.

It’s possible to perform the experiment with no mass if one moves from
locked to unlocked position after the check is made. So we add an extra
check after the subject moves to the starting target. This will be
annoying if it actually happens, but most of the time the second test
should pass silently.
Attempts to make the friction test easier.

Set acceptabel range to be a fixed width, rather than on a percentage
of the center.
Do the high grip force friction test first.

Friction test with high grip force is easier to succeed. So we do it
first to give the astronaut the idea.
Make *** Subject *** labels fit in window.
Add a bunch of maintenance tests.

Required for SVT, but probably useful to have on board anyway.