Continuous integration via Github Actions

[cqnykamp]

Added CI for both client and server apps.

Client checks:

• Prettier
• ESLint
• App can build

Server checks:

• Prettier
• ESLint
• App can build
• Tests pass

The server-side tests work by spinning up a local mysql db on the host computer.

[dqnykamp]

Cool. It looks like we have some linting work to do! We should add multi-reporter-config.json to .prettierignore, as it gets recreated by a cypress test runner in a way that prettier doesn't like.