Normalise error handling in the UI

[jvolker]

Following up from #12

@jmwohl:

The notifications package I was using hasn't been maintained and doesn't work, so either needs to be forked and fixed or swapped out for another package

This is for the success/info/error notifications for the UI (not the error warnings in edit forms).

I decided to just pull the redux-notifications code into our project rather than use the unmaintained dependency. I've updated the code a bit so we should have working notifications again now.

Not sure if this is new or what redux-notifications was using anyway under the hood, but what about Bootstrap Alerts? https://getbootstrap.com/docs/4.0/components/alerts/