Asset hot reloading

[IntegratedQuantum]

Basic idea:
Register some monitors(I think that's what they are called) for each file that was loaded.
When a file changed there is two options:

1. I could trigger a complete asset reload. This might be expensive though.
2. I could selectively reload the changed asset, but that requires some bookkeeping.

In any case this would be insanely useful for designing assets

Potential problems:
Changes to biomes would require a complete world reload
Changes to some block data would require a complete mesh reload