refcount SystemBodys and handle decoupling them them from the StarSystem when it dies. now they can outlive their StarSystem
LuaObject restructure

- No more LuaUncopyable hack
- No more LuaAcquirer hack
- Separate wrapper objects for different object ownership models
- Wrapper objects are userdata - no more integer ID objects
- Simplified registry structure
get ShipFlavour out of the shipyard. add a light ShipOnSale structure to hold info about ships in the shipyard
no more ShipFlavour
color->lua conversion method
scenegraph lua setup and model stubs
Merge branch 'lua-cleanup-2' into model-skin
make ModelSkin RefCounted so that Lua can use it
randomise colour on new ships
Ship.skin attribute
get the skin through to the model spinner