Made a whole lot of these classes Serializable, as I'm looking into
using serialization to store map info.
A different attempt at encoding/decoding stage files under
construction... We'll see if it works properly once it's finished.
EntitySimulator implements Iterable<Entity> now.
Added a link() method to Entity to allow entities to be linked with a
common interface. Relevant entity types now implement link().
added more serialUIDs
cleaned up iterator code
added more getters and setters for needed things