Enable one Step per contact

[renatomassaro]

Initially the player could only ever be in one step. This would not work quite well with our multiple NPC, GTA-like storyline system, so it was revamped to enable one step per contact. So, basically, the player can progress on the storyline using whichever NPC she'd like at a given time.

Incidentally includes some improvements that came along the way.

This change is 

[sourcelevel-bot]

Ebert has finished reviewing this Pull Request and has found:

• 1 fixed issue! 🎉

You can see more details about this review at https://ebertapp.io/github/HackerExperience/Helix/pulls/382.

[renatomassaro]

Reviewed 42 of 44 files at r1, 3 of 3 files at r2.
Review status: all files reviewed at latest revision, 4 unresolved discussions.

---

lib/story/query/story.ex, line 23 at r2 (raw file):

  @spec get_steps(Entity.id) ::
    [StepInternal.step_info]
  defdelegate get_steps(entity_id),

docme

---

lib/story/websocket/requests/email/reply.ex, line 25 at r2 (raw file):

      update_params(request, params, reply: true)
    else
      {:error, reason = :bad_contact} ->

Mention this error on endpoint doc

---

priv/repo/story/migrations/20180201171652_story_contact.exs, line 12 at r2 (raw file):

      add :contact_id, :string, primary_key: true

      add :step_name, :string

NOT NULL

---

test/support/story/setup/manager.ex, line 46 at r2 (raw file):

    {manager, related}
  end

extra line

---

Comments from Reviewable

[renatomassaro]

Reviewed 4 of 4 files at r3.
Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable