Format with Fourmolu and ch-hs-imports

[ocharles]

Fixes #123

[ocharles]

I'll merge this once other PRs are closed.

[fisx]

might not be needed here, but there is a tool for rebasing formatting pull requests over others that helped us with introducing ormolu: https://github.com/wireapp/wire-server/blob/develop/tools/rebase-onto-formatter.sh

it's a really neat and well-documented trick, so just reading it without needing it might be worth it. :)

shoutout to @mheinzel o/