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.

{{ cookiecutter.project_slug }}/src/components/cwusers/CWUsers.tsx

@@ -18,7 +18,7 @@
       <h1>CWUsers from {cwserver}</h1>
       <ul>
         {cwusers.map((cwuser) => (
-          <li>
+          <li key={cwuser.login}>
             <BsPersonCircle /> - {cwuser.firstname} {cwuser.surname} (
             {cwuser.login})
           </li>