Rectify plugin classloader to let FML mods see its classes

[Aizistral]

General idea is to replicate what can already be achieved on 1.12.2 with combination of:

1. This small coremod with a single mixin: https://github.com/terrainwax/ForgeCanCallBukkit
2. Custom launchwrapper: https://github.com/terrainwax/LegacyLauncher

Launchwrapper version hopefully matches for both MC versions. However, it appears that bukkit plugin classloader in Thermos/Crucible has some differences from whatever above patch was designed to handle, and in my tests done with Thermos setup specifically that patch didn't work.

For reference, here is the mixin I created:

Log output indicated that it applied successfully:

Here was some code to test if it works as intended:

Here was exception reminding me that life is never that easy: