Migrate pgn-viewer to Typescript

[mliebelt]

The migration of pgn-reader was successful, so the logical next step.

Things to do:

• [x] Change the js files (if possible) to ts
• [x] Implement a base build process, that uses the learning from pgn-reader. But keep Webpack up and running.
• [x] Have a look at the libraries used, if they can be migrated as well.
  • [x] Check how mousetrap-ts can be enabled to stop working in text fields
  • [x] Ensure that smoothscroll can be imported and used
  • [x] Chessground is already in typescript
  • [x] roddeh-i18n works without a change

[mliebelt]

I think that most of the job is done. I will find glitches and flaws later, that need action due to the usage of Typescript, but I don't know what to do from now on. Therefore the issue is closed.