Work on adding support for OnSerialize() and OnDeserialize() for script components.

This is work towards addressing issue #88.

All that's really left is calling OnDeserialize() properly, but the issue is
that at the point at which it should be called, the node has not yet been
added to the scene, which in turn means the scripting environment is not
available to the component.
Change the way serialization and deserialization is done in Scene.

The is work towards addressing issue #88.

This changes the serialized format of scenes. Old scenes will crash on load.
Have OnDeserialize get called when opened by the scene editor.

This partly addresses issue #88. Still needs testing for scenes that are loaded
from outside the editor before marking this issue as resolved.
Change the way scenes are loaded in the sandbox.

This is required for script-side OnDeserialize to work. Related to issue #88.