Improve Redux test utilities

[lindapaiste]

Previously submitted as part of #2054

Allows for better testing of connected components.

Changes:

• reduxRender uses the same configureStore function as the app itself, meaning that the test Redux store will have the same middleware. This is necessary in order dispatch thunk actions from tests.
• The return value of reduxRender includes the store instance, as shown in the Redux docs. This means that tests can call store.dispatch() or store.getState(), although interacting with the document (end-to-end testing) should be preferred over interacting with Redux directly.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123