ModelDoc Improvements

I made some more improvmenets to ModelDoc this month. ModelDoc is the tool used to create/import models into Source 2.

By default ModelDoc fbx import only supports one bindpose. And that's probably fine if you're making all your models bespoke.. but if you're like us and importing models from other places, you're going to run into problems.

The rust crossbow viewmodel was broken because of this. That's now fixed.

There's now a viewmodel camera mode, which just locks the view to zero, this is useful for seeing how your viewmodel looks like in game and if you'll need to offset it. There's probably some other useful camera modes I can add in the future.

I added support for importing Source1 models. It's debatable if we should even include this because we want to encourage new assets to be made, not just for old assets to be ported over. The way I see it though, people are gonna do it anyway and I'd rather people not download old janky MDL decompilers.

This was broken. It didn't visualize or calculate the mass info so I fixed that up.