FuelFlowSimulation optimizations.

Most importantly, the calculation of the FuelNode.decoupledInStage values
was changed from an O(N^2) algorithm to an O(N) one. Based on profiling
this cuts the cost of StartSimulation by 50-70%.
Faster version of UserPool.RecursiveUser.

Profiling showed that the previous version could be a slight performance problem.
Allow changing SmartASS target while another module steers
Add Surface Velocity Targets to SmartASS