rename ShipSpinner to ModelSpinner and make it take a model and a skin
make the old spinner take model+skin as well
remove Lua ShipFlavour stuff
remove per-flavour price (including part exchange). economy is broken anyway, we can do this better next time
remove regid from flavour, just make it the label
remove ShipFlavour from Ship and clean up ShipType use a bit
get ShipFlavour out of the shipyard. add a light ShipOnSale structure to hold info about ships in the shipyard
no more ShipFlavour
rename onShipFlavourChanged event to onShipTypeChanged