Update asset references in models

[LPGhatguy]

We have a clear plan for how to handle assets that are used programmatically, but that's only a small fraction of the way that assets are used in Roblox.

It would be a good idea to build a tool that can traverse models and places to update their asset references when they need to be updated. This might not fit into Tarmac, but Tarmac should be able to produce the data needed to build a tool that can do this.