Many little improvements

Don't hesitate to review commit by commit.

Further improvements could be made: I think that we could enforce using prettier and jest for example.

requested review from @famarger

assigned to @fbessou

added 2 commits

• 992236a51e3a - fix(CWUser): add missing `key` prop to list elements
• a0110cd1cb0d - fix: use new react-dom api to create the app root

Compare with previous version

I added issues #1 (closed) and #2 regarding your description. Otherwise, this MR looks good to me, :) let's merge this. Thank you for this!

merged