Typescript conversion (second attempt)

[emma-sg]

Convert the codebase to Typescript!
Closes #198

Changes

• Convert entire project to TS using some tools from https://github.com/stripe-archive/flow-to-typescript-codemod
• Set up ESLint with rules from replaywebpage, and autofix a bunch of things
• Remove checked-in built files
• Replaces outdated node-sass with sass

Testing

• Main build runs succesfully locally
• CI runs successfully
• Electron app builds successfully
• Manual testing

Merge Blockers

• Required changes to replaywebpage published on NPM
  • Update NPM packaging, linting, and a bunch of types replayweb.page#275 merged
  • 2.0.0 branch published to NPM
  • Configure package exports explicitly replayweb.page#336 merged
  • 2.1.x published to NPM