Move definition of Warpable's popupMenu to Squirrel initializer

We should make all popup menus scripted.
Translate warp menu item title to Japanese

This is a made-up benefit of scripting.
Add experimental property map feature to CoordSys

Star demonstrates its functionality by overrididing it.
Make property accessors take CoordSys argument

We could call sq_refobj() in all accessor handlers, but it would not
conserve const qualifier.
Add mass accessors and orbits() method to Astrobj for Squirrel
Add propertyMap to OrbitCS and Astrobj
Add warp destination accessors to Warpable for Squirrel
Make OrbitCS constructible from Squirrel scripts

Also moved orbits() method from Astrobj to OrbitCS.

Also added multiple definition guards to sq_define() static member
function of OrbitCS, Astrobj and Star.
Move star materialization code to Squirrel
Delete redundant sq_get() from Astrobj and Star
Add tostring() method to CoordSys for Squirrel

It's just the same logic as Entity's one.