ESLint transition: update code so "no-throw-literal" passes

[cbraynor]

This issue relates to the no-throw-literal rule.

During the transition from TSLint (now deprecated) to ESLint for typescript linting we introduced some new rules that don't yet pass and added a temporary override in the .eslintrc.json file to temporarily disable them.

This issue covers removing that temporary override and any changes to the typescript code required to get the rule passing. Use npm run lint to run the linter and once you've done changing the typescript don't forget to also run npm run build to reflect the changes in the built javascript (which also needs to be checked in).