Change initial speed between Enterprise and Klingons

* erltrek.hrl: add #ship_def.initial_speed
  (This value differs between Enterprise and Klingons:
   Enterprise: 0.9, Klingons: 0.3, so Enterprise moves
   three times faster than Klingons right now)
* erltrek_ship.erl: use #ship_def.initial_speed as the
  initial value for #ship_state.speed