Remove ModuleBase#Self type member, use implicit priority-based scheme instead

[neko-kai]

How it works: for a type ModuleDef <: Module <: ModuleBase the priority of companion object searches is ModuleDef -> Module -> ModuleBase such that if we launch a search for ModuleMake[ModuleDef, T], companion object of Module will have a higher priority that companion object of ModuleBase resulting in the instance ModuleMake[Module, Module].

Unfortunately we also have to add an implicit rule transforming any ModuleMake.Aux[X, T] into ModuleMake[T] - to be able to use instance of ModuleMake[T] when there's only an instance of ModuleMake.Aux[X, T] - because the X parameter shouldn't stop us from using the instance, it's only there to make the search happen in the companion objects, i.e. it's a pure phantom parameter, but there's no way to express it in Scala currently.