Reduce bundle size

[cmitz]

We need to reduce our bundle size. It's now a whopping 5 MB.

Some things we can do:

• [x] Replace EmojiOne with unicode-only or another, much smaller, library (Twemoji?)
• [x] Slim down bundled FontAwesome package (maybe whitelist like this)
• [x] Remove jQuery
• [ ] Remove MomentJS in favour of a smaller library

There's probably a lot more, but that'd need some investigation using this: https://codingitwrong.com/2018/09/02/ember-bundle-size.html

[Matthijsy]

Also consider something for showdown.js, this is even bigger than momentjs