New JavaScript based system for implementing CoreMods.
Why?
Because it means that it's a lot easier to manage the lifecycle correctly. We can isolate CoreMod logic to the proper ClassLoading contexts without effort on the part of the Modder.
It hopefully also communicates that CoreMods are strictly arms-length : they operate on classes as they load only - changing structures and behaviours through that means.
This is connected to Forge and FML through the CoreMod SPI being implemented in new Forge.
