Implement unit, feature and object classes under a unified interface

[gajop]

Should allow us to write better code with more polymorphism.
We can also put "area" under the same interface, and create composite classes with object groups

[gajop]

We should be very careful here with how we create metatables. If we are not careful, they are likely to produce very memory expensive objects, much like it was the case with chili classes.

We are probably better off creating some very simple metatable system and have all objects share the same metatable