Improve typing of StoreEnhancer

[Igorbek]

Following up #1526 (comment) here is a PR that enhance typyings for StoreEnhancer.

• make StoreEnhancer to be parameterized by state type, because it's always being called with known type of the state, so that it opens a way to create state-specific enhancers
• when a generic version of StoreEnhancer is needed, newly introduced GenericStoreEnhancer can be used, which a function with same signature but has a state type parameter; obviously it's assignable to any typed store enhancer
• StoreEnhancer exposes a StoreEnhancerStoreCreator<S> as a result, that is a stricter version of StoreCreator which strictly expects to get a reducer and initial state (not optionals)
• applyMiddlewares now returns GenericStoreEnhancer as the middlewares are generic
• tests that show/prove usage of the new signature have also been added

/cc @aikoven

[aikoven]

Looks great to me.
Cc @ulfryk @Pajn

[ulfryk]

Absolutely 👍