Map props (Treasure chests, corpses and interactables)

[brandc87]

Just documenting packets and features that require work/implementation as I work through code. Seems as though this was implemented as a Treasure Chest system in the old source, although it seems a little deeper.

Maps are missing "PropObject", an object players interact with (opening a chest, searching a corpse etc.)

Related server packets: 153 155 70 154