Add property iterator to CoordSys for Squirrel scripts

Now we can iterate over all properties of a CoordSys by foreach statement,
including additional properties defined in derived classes.
This could not be easily done by other means.
Specifically, conventional scstrcmp chaining disallow usage of iteration
because Squirrel VM has no idea what property the object has.  Defining
property map has been mandatory for this feature.
Add property displaying window for CoordSys objects

You can show the window by right-clicking on an item in a warp destination
window.
Add documentation comment to GLwindow definition for Squirrel
Change CoordSys.name from methods to property in Squirrel

The method has been working without problem, but now we want to iterate
name as a property in a foreach statement.
Move child, next and parent methods to property for CoordSys
Add CoordSys.alive property to return availability of the object

CoordSys can be deleted in the game while Squirrel VM holds a reference
to it.  Our WeakPtr<CoordSys> resets references to destroyed object, but
Squirrel VM thinks that the instance is not yet deleted.  We'll mark
false to alive property of such an object.
Prevent multiple definition of CoordSys class in Squirrel VM

The class has been defined multiple times as derived classes demands its
definition.  It results that each derived classes have different base
class entities (although the behavior looks the same), which makes
instanceof operator yield unexpected value.
Allow CoordSys information window walk on CoordSys tree

The window shows child, next and parent pointers to related CoordSys
objects.  Now these pointers become links that clicking on them brings
you to the clicked object.

General users may feel confused to navigate through pointers, since the
structure of the CoordSys tree is a bit counterintuitive.