Invite devroom managers, even without scheduled talks

[reivilibre]

Currently in the conference-bot, people only exist within talks.

But if you want to invite the devroom managers to the devrooms (which have been confirmed) but no talks have been confirmed yet, you currently can't.

This PR makes it so that auditoriums can carry a record of extraPeople to fill this gap.

We also pull in the extraPeople from the FOSDEM-JSON schedules.

  "tracks": [
    {
      "id": 42,
      "slug": "example",
      "name": "Example devroom",
      "email": "[email protected]",
      "type": "devroom",
      "managers": [
        {
          "person_id": 1,
          "event_role": "coordinator",
          "name": "person",
          "email": "[email protected]",
          "matrix_id": "@person:fosdem.org"
        }
      ]
    },
    ...
  ]