Syntax highlighting of JSON in the preview.

Not functional yet

simplify webpack setup

See merge request !24

Bump PS to 0.13.6

See merge request !25

(cherry picked from commit 2e05fc87)

* make webpack dev server work again
* use the purescript compiler output CommonJS modules from src/index.js
* add prebuild "yarn compile" script
* with "yarn dev", you now only need to run a purs ide plugin or run "yarn compile"

Merge branch 'dev-async-file-upload' of ssh://gitlab.iscpif.fr:20022/gargantext/purescript-gargantext into dev-async-file-upload

Also, html code element edits text properly (no state, just refs which
prevents cursor jumping).