Upgrade the react-mde (markdown editor) to v6.0

[Errorname]

Is your feature request related to a problem? Please describe. The markdown editor used in FAQ, react-mde, has seen a lot of improvements lately. We should upgrade to its 6.0 version to get them.

To do:

• [ ] Upgrade to 6.0
• [ ] Remove font-awesome dependency
• [ ] Add emoji button (https://missive.github.io/emoji-mart/)

Additional context react-mde is currently in 6.0.0-alpha.1. But hey, I like to live dangerously ¯\(ツ)\/¯

Update 12/01/19: Looks like react-mde is now a stable release!

[Errorname]

Closed by #193