extract Module from Provider into an interface

The attached code fixes issue #29 and prepares us for the upgrade to Dagger 1.0.

`denominator.Provider` can no longer be a base implementation of `dagger.Module` as starting in Dagger 1.0, this pattern no longer compiles.  The better way to accomplish the task is to have `denominator.Provider` reference its configuration, which is the essence of this change.