This makes the code a bit shorter by not having to use `props.` all of
the time. Also make everything VoidFunctionComponent while we are
touching this.
This uses the real rootReducer to populate the initial state in the test
AsyncSaga. This way we don't have to populate default values. Since it
isn't used often, we can omit the parameter and just call the updateState()
method after creating the object if modifications are needed.
The pattern we were using for actions required actions to be defined in
three places, an enum member containing the type string, an type
definition and a function. This combines all three of these into one by
using a helper function based on the ideas from [1].
[1]: https://phryneas.de/redux-typescript-no-discriminating-union
David Lechner