Convert all code to Typescript

# User Story

> As a developer, I want all code on Alley Scripts to be written in TypeScript with types exported so that I can use it in my TypeScript project.

# Acceptance Criteria

- Update all JavaScript code to TypeScript
- Remove support for JavaScript where necessary (e.g., ESLint configs, Webpack, etc) and assume that all code will be `.ts` or `.tsx` moving forward
- Update README to indicate that the project is 100% TypeScript
- Explore use of ts-jest and ts-node to ensure all files can be TypeScript