WIP: frontend: extract scripts

[Spoonbaker]

This is a work in progress; I am creating this as a starting point for the frontend team. This can be merged after #36; The target branch will be updated automatically.

Also note that currently all buttons that rely on onclick= don't work, as the dev CSP blocks them. The onclick= handlers will need to be changed, see below.

Tasks that need to get done:

• Don't set .innerHTML anywhere
• Turn onclick= handlers into <element>.addEventListener("click", <function>)
• Make rpm run check pass
  • The @ts-ignore directive is temporarily hiding some errors. Remove the directive and fix the errors
  • Remove unused declarations