User model expansion and decomposition

[s2t2]

Per #6 (comment), here are the user attributes collected by the client app during the user registration process:

Consider adding oauth-related attributes. And figure out a way to incorporate the preference-related attributes while balancing needs for flexibility and security.

Consider splitting the User model into component User, UserAuth and UserPreference models. Maybe something like this:

{
  username: "____",
  first_name: "____",
  last_name: "____",
  bio: "_________",
  image_url: "_____",
  hero_url: "_____",
  birth_year: 1975,
  professions: ["Student", "Performer", "Instructor"]

  auth: { // <--- proposed attributes for the `UserAuth` model
    email: "____",
    password: "____",
    confirmed: true,
    oauth: true,
    oauth_provider: "Google",
    role: "User",
    access_level: "Full"
  },

  preferences: { // <--- proposed attributes for the `UserPreference` model
    visible: true,
    composers: ["Bach"],
    performers: ["Dave Matthews"],
    periods: ["Classical", "Contemporary", "Baroque"],
    instruments: [{
      name: "Guitar",
      owned: true,
      owned_models: ["Gibson ABC", "Fender Blah"]
    }]
  }
}

... or maybe something like this instead, with User, UserProfile, and UserMusicPref:

{
  username: "____",
  email: "____",
  password: "____",
  confirmed: true,
  visible: true,
  oauth: true,
  oauth_provider: "Google",
  role: "User",
  access_level: "Full"
  
  profile: { // <--- proposed attributes for the `UserProfile` model
    first_name: "____",
    last_name: "____",
    bio: "_________",
    image_url: "_____",
    hero_url: "_____",
    birth_year: 1975,
    professions: ["Student", "Performer", "Instructor"]
  },

  music_preferences: { // <--- proposed attributes for the `UserMusicPreference` model
    composers: ["Bach"],
    performers: ["Dave Matthews"],
    periods: ["Classical", "Contemporary", "Baroque"],
    instruments: [{
      name: "Guitar",
      owned: true,
      owned_models: ["Gibson ABC", "Fender Blah"]
    }]

  }
}

[s2t2]

For now I am storing everything except musical preferences / survey responses on the user model, and we can tackle the preferences separately. And we can split the model up later if necessary.