Add importing html and save it to Article

Additionally defines a wizard logic which is partially unused yet.

lib/outlook/internal_tree/raw_internal_tree_schema.ex

@@ -0,0 +1,29 @@
+defmodule Outlook.Articles.RawInternalTreeSchema do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  alias Outlook.Articles.RawInternalTree
+
+  embedded_schema do
+    field :tree, RawInternalTree
+  end
+
+  @doc false
+  def changeset(raw_tree, attrs) do
+    raw_tree
+    |> check_sibling_collocation(:tree)
+  end
+
+  def check_sibling_collocation(changeset, field) when is_atom(field) do
+    validate_change(changeset, field, fn field, value ->
+      case value do
+        true ->
+          []
+
+        false ->
+          [{field, "html should be useful"}]
+      end
+    end)
+  end
+
+end