Add :eph field to %TranslationUnit{} and remove :sibling_with

Using :eph from now on to store ephemeral data like :sibling_with. Additionally
added cleaning up :eph before saving to db. And renamed InternalTree.Basic
to InternalTree.RawInternalBasic to make clear that it contains function
for an intermediary tree structure.

lib/outlook/articles/internal_tree.ex

@@ -3,6 +3,7 @@ defmodule Outlook.Articles.InternalTree do
 
   alias Outlook.InternalTree.InternalNode
   alias Outlook.InternalTree.TranslationUnit
+  alias Outlook.InternalTree.Basic
 
   def type, do: :string
 
@@ -16,7 +17,10 @@ defmodule Outlook.Articles.InternalTree do
     {:ok, Jason.decode!(tree, keys: :atoms!) |> from_json}
   end
 
-  def dump(tree) when is_list(tree), do: {:ok, Jason.encode!(tree)}
+  def dump(tree) when is_list(tree) do
+    {:ok, Basic.clean_eph(tree) |> Jason.encode!()}
+  end
+
   def dump(_), do: :error