refactor: migrate to NgRx v8 creators

[wesleygrimes]

• migrate to use createAction instead of classes, enums and type unions
• migrate to use createReducer over switch statements
• migrate to use createEffect

Digging through the code I saw some OOP concepts at play with regards to the HeroAction and VillainAction abstract classes. This played nicely into creating a couple higher order functions that can be composed. As such, I created create*Action and create*ErrorAction for both heroes and villains.

The one area I did have a hard time in converting was the effects that used the toAction helper. Once we release in NgRx the mapToAction operator, this will become a lot easier.

Another option would be to create a "higher order" effect like I propose here: ngrx/platform#1826 To standardize the way effects are composed.

Let me know what you think and if you have any questions.