Add a notes field from submitters for the driver

[lamarqua]

I think it would be useful to have a notes field so that we can add notes for the driver like, "no intro", "youtube link is timestamped, song ends at 4:35, please stop it there" or anything really.

[lamarqua]

Suggestion for UI:

• add a "notes to the submitter" textarea field in the submission / edition form. Add specific placeholder text as to what to write in the notes field. (So submitters know that this will be shown to the driver only) Example placeholder:
  "Write in here notes to help the driver process your song, for example 'no intro', or 'play this one in round 3', etc.")
• make this notes field visible for the driver, but not to the person browsing the archives. This field is intended for helping the driver organize the session, stuff that the submitter want to be displayed in the archives should be in the suggested context field (Add an intro / context field for archiving purposes #15)