Use OperationFinder instead of module method

[marten]

OperationFinder uses a reduce to "recursively" find operations through operation finders scoped to ever deeper nested namespaces.

As is, this approach is probably overly complex. But this approach allows us to in the future, inject at any point in the chain some custom lookup strategy. For instance, we might want to add support for operations that are defined as a single class method, which would make Pavlov more light-weight for simple queries.

[markijbema]

Really liking this refactor.

[marten]

@markijbema your comments have been fixed