Replace Lua ship stats tables with properties

We all know `m_shipstats` is dumb. Dumber still is exposing it to Lua. So this gets rid of the Lua `GetStats()` method and moves the various values onto the ship object itself as properties.

Names have been kept, but it does break old code. Its easy to fix at least. And as properties they can now be used in UI binds, which is the point of all this.

While I was in there, I got rid of `maxCapacity`, `maxFuelTankMass` and `fuelUse` since those values don't change and are available in the relevant `ShipDef` anyway.

I'm deliberately not doing anything about `m_shipstats` here. Disentangling it will be hairy and I don't need it right now.