Item and Block wrappers

[trainb0y]

Currently custom items and blocks are represented by string ids, which is... rather dumb.

There should also probably be wrapper classes that define a "block", or an "item stack" but doesn't care whether it's vanilla or custom.

This is one of the reasons id like to consider switching to serverside fabric, as items and blocks could be registered mostly normally using something like Polymer or PolyMc