Review linting implementation and resolve errors

[samwarwick]

This issue contributes to #157

A TSLint configuration file is present in the repo tslint.json. However TSLint is not installed in package.json and there are no scripts to run it.

Executing npx tslint --project . reports over 400 errors.

TSLint was deprecated in 2019 in favor of ESLint which is the current recommendation for TypeScript linting.

AC for this issue:

1. Upgrade the linter from TSLint to ESLint
2. ESlint is installed with package.json
3. Add a script for running the linter e.g. npm run lint
4. Base initial linting rules on the current tslint.json (the rules can be reviewed/revised later)
5. Resolve all linting errors.