Error message display.

[louh]

1. Store

• Components that report errors should put them in the Redux store. The components do not necessarily have to know about the store. We could write a single module that exports a addError() function that wraps the functionality for adding data to the store, so that the Redux store dependency is not baked into every component.

2. View

• The UI renders the error somewhere:
  • Message in the control panel?
  • Modal?
  • Toast?