Do not throw error when a CoordSys object in Squirrel VM become NULL

Now that CoordSys object tree is fairly dynamic, we cannot assume that
these objects are stationary.  Specifically, symbolic bookmarks can
easily become broken.  The callers of CoordSys::sq_refobj() should take
care of returned NULLs appropriately.
Make extent, isolated and cs_radius properties accessible from Squirrel
Make materialized star systems have enough cs_radius as a solar system

This will make the solar system browser work fine with those systems.
Expose fontwidth() API to Squirrel scripts
Add column headers to warp destination selection window

Clicking on a header makes the list be sorted by the column value.
Clicking the same column again reverses the order.

We would also like to change column order and widths, but it's not
implemented yet.
Fix random star labels fail to display on correct position seen from Sol

We have not properly calculated transformation matrix from the universe
to the local (viewer's) CoordSys.  This issue has not been exposed since
it looks fine when we're viewing from a CoordSys having the same
orientation as the universe, but it's obvious when we're in Sol.
Non-random stars have not had this problem.