Implement reducers with handleActions

Currently most of our reducers are implemented as a big switch statement, which is unwieldy and hard to read. Instead, use the handleActions() helper in redux-actions to implement the reducer as a map of action names to reducer functions.

We should follow the pattern of using the action creator function itself as the map key, allowing us to avoid hard-coding string literals containing the action name.

See the console reducer for an example of the desired implementation.

Testing

Since our goal here is merely to refactor the reducers, not change their behavior, all existing tests should pass after a reducer is refactored.

However, it might make sense to also port the reducer test to Jest after completing the refactor and confirming that the old tests pass with the new reducer implementation (this should be in separate commits).

Reducers to migrate

• clients
• compiledProjects
• console
• currentProject
• errors
• googleClassroom
• index
• projects
• resizableFlex
• ui
• user

Start with the completed example in src/reducers/console.js, then locate the unchecked clients, compiledProjects, currentProject, errors, googleClassroom, index, projects, and user reducers. Refactor them with redux-actions while preserving behavior, and run all existing tests to confirm they still pass; leave Jest test porting for a separate change.