Add missing specs for LazyProxy
Spelling
Implement respond_to_missing?

This makes it possible to retreive methods from the LazyProxy using #method.
This avoids issues with 3rd party code.
Remove duplication of default dependencies

Only rely on the default dependencies as defined in the classes initialize
methods instead of duplicating this knowledge inside the QuantifyMe module.
Move default MetricSerializer deps into class
Pass UserGateway deps in a Hash

This unifies how dependencies are injected into other objects in the system.
Move default UserGateway deps into the class