Use Redux to store client application state

[mrgnr]

Redux provides a centralized store for application state. Previously, state that needed to be shared by multiple components was "lifted up", but this results in passing lots of data and callback functions down through the component hierarchy via props. Keeping state in a central location alleviates this problem, which would probably become increasingly worse as more components are added to the UI.

In addition to the core Redux package, the following dependencies have also been added:

• React Redux -- makes it easier to integrate Redux into our React components, namely via the connect function which allows us to pass Redux state and actions via props
• Redux Toolkit -- organizes Redux code into slices and reduces boilerplate for action creators
• Redux Saga -- middleware that handles asynchronous calls and side-effects. We treat interaction with the RTC Manager as a side-effect from the perspective of Redux, so this code runs in a saga.