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/internal_tree/internal_node.ex

@@ -1,4 +1,4 @@
 defmodule Outlook.InternalTree.InternalNode do
  @derive Jason.Encoder
- defstruct name: "", attributes: %{}, type: :atom, uuid: "", content: [], sibling_with: nil
+ defstruct name: "", attributes: %{}, type: :atom, uuid: "", content: [], eph: %{}
 end