Changes

PSG: fix coast MaxT

makes MaxT the responsiblity of the Phase and not the optimizer.

previously, the calculation in the optimizer was dividing by zero
for coasts where minThrottle = 0 and that value just doesn't make
and sense.  so make the burn phase factory method responsible for
setting MaxT to be correct for a burn phase and adjusting by
minThrottle.
 (commit: d61ebb8)