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• Replaces outdated node-sass with sass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

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

Merge Blockers

• [x] Required changes to replaywebpage published on NPM
  • [x] https://github.com/webrecorder/replayweb.page/pull/275 merged
  • [x] 2.0.0 branch published to NPM
  • [x] https://github.com/webrecorder/replayweb.page/pull/336 merged
  • [x] 2.1.x published to NPM