Objects loaded before skybox don't set envMap

[jbaicoianu]

If an object in a room loads before the room's skybox is loaded, the object never gets its environment map set, so it looks too dark and doesn't reflect the environment

[jbaicoianu]

Fixed, we now fire a skybox_change eventr from the room object, and our objects are now listening for that event. This also means changing the room's skybox at runtime will be reflected for all objects in the room