improve workflow for adding new ships

[rlane]

Currently, to add a new ship you need to: (see a963669d155103fd77c578439da2cdabf150ec47)

• Add the specs to ships.lua.
• Add code to shipped AIs.
• Add a lot of rendering code.

We should move the ship vector art into data files so no Vala code needs to be modified to add a new ship.

[austinjames314]

How many new ships do you want to add? Do you envisage user designed ships, or is this just to ease development? How many ship types do you envisage?

[rlane]

I don't expect to add many more ships. I do want to make it easy for people to tinker with the game and improve on the current ship selection. I also think it would be interesting to allow scenarios to modify the ships table and add new ones.