New Entity/MapObject model.

[ZaneDubya]

Currently, the Map contains Tiles, which contain MapObjects. Each frame, each Entity adds (or updates?) its MapObject within the associated Tile. Then, on draw, the Tile draws all of its MapObjects.

The dual Entity / MapObject is unnecessary, and an artifact of my implementing Clint's XNA renderer (he used MapObjects, and I pretty much bolted on his code to the client without considering how to re-implement the way it worked to better fit the client's code).

Instead, each Entity should belong to/exist within one MapTile, and on draw, the MapTile should be able to ask the Entity for its 'EntityView' object, which describes how that entity should be drawn.

In short:
Old Model:
OnUpdate: Each entity creates a MapObject, which is added to Tile.
OnDraw: Tile draws all MapObjects.
New Model:
OnUpdate: nothing.
OnDraw: Tile requests a EntityView for each Entity within that Tile, and draws these EntityViews.

[ZaneDubya]

Noticed some weird rubber banding with new Position3D code. Probably introduced in f4d6bbf.

[ZaneDubya]

Completed in 5753068. Will not merge until deferred rendering is done.