At various places in our code that receive external inputs (eg.
WebSocket messages, messages from other frames etc.) we have to wrap
that handling in a $scope.$apply() call or similar in order to trigger
Angular's change detection cycle and sync UI components with the updated
state of the app after handling that input.

Since most changes to app state now happen as a result of a Redux action
being dispatched, we can use Redux' built-in middleware mechanism for
adding logic around app state changes.