Add mod manifest 'Monkeyfest' system for additional static metadata

[Banane9]

Add (option for) 'monkeyfest.json' at the root of mod packages that defines additional metadata for the mod.
This should work like the config system regarding safe loading of data even without knowing the full model - but read-only.

Standard data:

• IsGamePack bool (maybe rethink this too? - would replace the requirement for being in another folder)
• IsPrePatcher bool (maybe?)
  • could be used to split regular patchers and pre-patchers into separate packages to simplify how to reference them
  • that would make installation more complicated with more packages though...
    • @ColinTimBarndt's blursed suggestion: nested nuget packages - separate only for development
  • or keep the nested DLLs in the folder, but have the split packages for development
    • manifest could list the pre-patchers as well
• Tags / Categories
• ...