Fix '.' and '..' imports

[colin-grant-work]

What it does

Imports from index.ts files in the same directory as a file or a higher level almost always entail circular dependencies. That doesn't have to be a catastrophe, but it's not a good idea. This PR adds a lint rule forbidding such imports and fixes those cases that currently exist. This reduces the number of warnings from webpack from 95 to 81.

How to test

1. Assert that there are no more imports from '.' or from '..' in our code.
2. Add such an import to a file.
3. Observe that the import is treated as a lint error.
4. Check that the application builds and runs as expected.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[paul-marechal]

LGTM, the ESLint rule is like icing on the cake ;)