How to change the layout of a phonix controller

Normally, phoenix uses `web/templates/layout/application.html.eex`
as the default template.
To change the layout you simply add

plug :put_layout, {Phoenix.Controller.__layout__(__MODULE__), :partner}

on the top of your controller, just above the `plug :action` line. So a
controller could look like:

defmodule PlusandmoreElixir.UserController do
  use PlusandmoreElixir.Web, :controller

  alias PlusandmoreElixir.User

  plug :scrub_params, "user" when action in [:create, :update]
  plug :put_layout, {Phoenix.Controller.__layout__(__MODULE__), :partner}
  plug :action
...