erltrek_galaxy: support ship movements with impulse command.

Collisions are also handled.

Example output ;)

Command > s
Short range sensor scan
  0 1 2 3 4 5 6 7 8 9
0 . . E . . . . . . . 0  Stardate:      2000.02
1 . . * . . . . . . . 1  Position:      6,1/0,2
2 . . . . . . . . . . 2  Condition:     GREEN
3 . . . . . . . . . . 3  Energy:        5000
4 . . . K . . . K . . 4  Shield:        1000
5 . @ . . . . * . . . 5  Klingons:      46
6 . . . . . . . H . * 6
7 . . . . . . . . * . 7
8 . . . . . . . * . * 8
9 . . K . . . . * . . 9
  0 1 2 3 4 5 6 7 8 9
Starsystem Talos IV
Command > i 7 9
Command > info: {enter_sector,{sectxy,1,3}}
info: {enter_sector,{sectxy,2,4}}
info: {enter_sector,{sectxy,3,5}}
info: {enter_sector,{sectxy,4,6}}
info: {enter_sector,{sectxy,5,7}}
info: {enter_sector,{sectxy,6,8}}
s
Short range sensor scan
  0 1 2 3 4 5 6 7 8 9
0 . . . . . . . . . . 0  Stardate:      2000.32
1 . . * . . . . . . . 1  Position:      6,1/6,8
2 . . . . . . . . . . 2  Condition:     GREEN
3 . . . . . . . . . . 3  Energy:        5000
4 . . . K . . . K . . 4  Shield:        1000
5 . @ . . . . * . . . 5  Klingons:      46
6 . . . . . . . H E * 6
7 . . . . . . . . * . 7
8 . . . . . . . * . * 8
9 . . K . . . . * . . 9
  0 1 2 3 4 5 6 7 8 9
Starsystem Talos IV
Command > info: {enter_sector,{sectxy,7,9}}
info: {enter_quadrant,{quadxy,6,2},{sectxy,8,0}}
info: {enter_sector,{sectxy,9,1}}
info: {enter_quadrant,{quadxy,7,2},{sectxy,0,2}}
info: {enter_sector,{sectxy,1,3}}
info: {collision,s_klingon,{enter_sector,{sectxy,2,4}}}
s
Short range sensor scan
  0 1 2 3 4 5 6 7 8 9
0 . . . . . . . . . . 0  Stardate:      2000.50
1 . . . E . . . . . . 1  Position:      7,2/1,3
2 . . . . K . . . . @ 2  Condition:     GREEN
3 . . . . . . . . . . 3  Energy:        5000
4 . . . . . . . . K . 4  Shield:        1000
5 . . . . . . . . . . 5  Klingons:      46
6 . . . . . . . . . . 6
7 . . . . . . . . . . 7
8 . . . . . . . . K . 8
9 . . . . . . . . . * 9
  0 1 2 3 4 5 6 7 8 9
Starsystem Echo IV

As can be seen, it took about 50 seconds before hitting the klingon
(also note that the ship does not yet stop when reaching the intended destination).