Alternative ships need implementing

[tboho1]

There are currently 7 ship models in total. It would be great if these could be randomly assigned to each player at the start of a game.

Some ship designs require 2 thrusters instead of 1.

[chrisfarms]

probably dup of #62 (but this one better)

[ldunnplaymint]

Needs testing in a PR. We probably do not want to merge it so this is more of a bonus task