TODO

   1 Replace underscore by lodash (or better: ES6)
   2 Replace socket.io by Websockets ( https://www.npmjs.com/package/websocket )
   3
   4 time per question (in mode "one question at a time" from server...)
   5 compute grades after exam (in teacher's view)
   6 factorize redundant code in course.js, monitor.js and (TOWRITE) grade.js
   7   (showing students list + grades or papers)
   8 monitoring: main teacher should not be asked for pwd, and button "send feedback" hidden for others
   9 (or just disabled)
  10
  11 -----
  12
  13 Draft format (compiled to json)
  14
  15 > Some global (HTML) intro
  16
  17 <some html question (or/+ exercise intro)>
  18
  19     <some html subQuestion>
  20     * some answer [trigger input/index in answers]
  21
  22     <another subquestion>
  23
  24         <sub-subQuestion>
  25         + choix1
  26         - choix 2
  27         + choix 3
  28         - choix4
  29
  30         <another sub sub>
  31         * answer 2 (which can
  32         be on
  33         several lines)
  34
  35 <Some second question>
  36 * With answer
  37
  38 =====
  39
  40 questions group by index prefix 1.2.3 1.1 ...etc --> '1'
  41
  42 NOTE: questions can contain parameterized exercises (how ?
  43 --> describe variables (syntax ?)
  44 --> write javascript script (OK, users trusted ? ==> safe mode possible if public website)
  45 Imaginary example: (using math.js)
  46     <params> (avant l'exo)
  47     x: math.random()
  48     y: math.random()
  49     M: math.matrix([[7, x], [y, -3]]);
  50     res: math.det(M)
  51     </params>
  52     <div>Calculer le déterminant de
  53     $$\begin{matrix}7 & x\\y & -3\end{matrix}$$</div>
  54     * ...