Implement Majority judgment in responsive booth

This merge request implements Majority Judgment type of vote in new frontend, and it is now ready to be merged. For reference, here is the data structure for a question in election.json:

    {
      "type": "NonHomomorphic",
      "value": {
        "answers": [
          "candidate A",
          "candidate B",
          "candidate C"
        ],
        "question": "Question title"
      },
      "extra": {
        "type": "MajorityJudgment",
        "blank": true,
        "mentions": [
          "Excellent",
          "Très bien",
          "Bien",
          "Assez bien",
          "Passable",
          "Insuffisant",
          "À rejeter"
        ]
      }
    }