Homebase and model things

* Adds the C-306 "Homebase" (Aurora) class capitals - slow, massive and heavily armed, monsters worthy of the name. With 64 engines and 32 hardpoints they reach the limits of what spaceships are capable of in three galaxies
* Changes specialvoxel-prefixes so 0xFFFFFF is a valid color
* Turns out  using mass-independent engines also requires you to create an engine for each ship. Using a mass-based approach probably is "more natural", because at least with the fighters mass grows about equally to engine count, resulting in credible speeds. They use maxMass now though to avoid targets becoming indestructible because they were moving too fast (one enginevoxel left) (#452)