`load_before` should allow setting the same mod as `optional_dependency` or `dependency`

[KANAjetzt]

Right now, load_before is equivalent to an optional_dependency, but in most cases, mods using load_before will depend on the mods in load_before. If the mod is loaded without the mod in load_before, it will most likely crash the game.

So, two options:

🎉: Just add the dependency check for load_before, i.e. don't load it if the dependency is missing.
🚀: Add the option to set the load_before mod also in optional_dependency and dependency. This is probably not as nice because we need to add additional checks in the existing dependency handling, as usually the dependency should load before the dependent mod.