Require state to be Equatable

[StevenLambion]

The PR requires the state to be equatable. This allows SwiftDux to perform better change tracking and reduces the need of Connectable.updateWhen(action:).

Work Performed

• Added Equatable to StateType
• Changed State type alias name on Connectable to Props to reduce naming collisions.
• Fixed equatable support for OrderedState.

[codecov-io]

Codecov Report

Merging #26 into master will decrease coverage by 0.09%.
The diff coverage is 25%.

@@            Coverage Diff            @@
##           master      #26     +/-   ##
=========================================
- Coverage   77.57%   77.47%   -0.1%     
=========================================
  Files          19       19             
  Lines         486      484      -2     
=========================================
- Hits          377      375      -2     
  Misses        109      109

Impacted Files	Coverage Δ
Sources/SwiftDux/Action/ActionSubscriber.swift	92.85% <ø> (ø)	⬆️
...wiftDuxExtras/Persistence/JSONStatePersistor.swift	66.66% <ø> (ø)	⬆️
Sources/SwiftDux/Middleware/Middleware.swift	100% <ø> (ø)	⬆️
Sources/SwiftDux/State/IdentifiableState.swift	0% <ø> (-33.34%)	⬇️
...es/SwiftDuxExtras/Persistence/StatePersistor.swift	84.61% <ø> (ø)	⬆️
Sources/SwiftDux/Store/StoreReducer.swift	100% <ø> (ø)	⬆️
Sources/SwiftDux/Store/StoreActionDispatcher.swift	31.57% <0%> (ø)	⬆️
Sources/SwiftDux/Store/Store.swift	94% <100%> (ø)	⬆️
Sources/SwiftDux/State/OrderedState.swift	81.45% <100%> (ø)	⬆️

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