Ship.lua: Add some safety against nil systems in the hyperspace interface
Consistently use StarSystem throughout the new Hyperspace stack
Ship.lua: Add a CanHyperspaceTo(system) method
LuaShip: Remove obsolete HS interfaces
Replace ResetHyperspaceCountdown calls by AbortHyperjump ones
WorldView: Use polling on Lua to get the hyperspace state
WorldView: Go in Hyperspace by calling the Lua HyperjumpTo method
{Ship,Player}.cpp: Remove unused and obsolete HS methods