BSP Diff Viewer

[tsa96]

Add a page that can loads two BSP files and generates some kind of Git-like diff between them. Some lumps probably change weirdly (idk if VRAD is even deterministic), but changes lumps we manage would be super useful.

Suggested by OzxyBox as a useful tool for future Chaos compiler improvements (ask in red for more details)

[tsa96]

Do we still want this? Seems like a lot of UI work, and suspect existing diff viewers could do a better job anyway.

Note that we already support exporting a JSON file that serializes every aspect of BSP files we parse.