Valve normalization and pmssc startup fix.

- Now that we have leds on the valves I can see what's going on. There's
  a much better description of what's happening in the code now.

- Added nervous_system::pump_both to turn on negative pressure to all lines.
  This may be used just when we are arm switching.

- Experimentation with different pump settings at arm switch time.

- Fixed bug with startup - pmssc servos weren't getting any initial
  pwm settings because the pmssclib dropped pwm values on the ground
  before connection, and then during connection it would just turn the
  thing on. I added code to the pmssc to cache the duty_us and then
  set it in ::connect just before turning the pwm on.