Decide on and Implement a Immutable Library to Prevent Modifying Existing State

[lalexgap]

Currently we rely on convention to make sure we don't modify existing state objects in reducers. If we do this by accident we can possibly cause painful to debug issues.

We should probably use a library that ensures the existing state is immutable. Redux has a list here:
https://github.com/markerikson/redux-ecosystem-links/blob/master/immutable-data.md#immutable-update-utilities