Consolidate feature interfaces

# Overview

Over the past couple of years, a set of abstractions has been introduced to enable more flexibility and maintainability. This has generally gone through the process of pulling the code out, adding an interface to abstract it, and then hooking it up. This has led to a set of features that can probably be reconciled (and exposed) to simplify an implementation of custom behavior.

- [ ] Saving is only partially consolidated with two interfaces: `ISaveFeature` and `IPackageSaveFeature`
- [ ] Eventing has a few ways to implement it and should be consolidated (and only a single pattern established)