add context notes

lib/memex/contexts/context_note.ex

@@ -0,0 +1,21 @@
+defmodule Memex.Contexts.ContextNote do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:id, :binary_id, autogenerate: true}
+  @foreign_key_type :binary_id
+  schema "context_notes" do
+
+    field :context_id, :binary_id
+    field :note_id, :binary_id
+
+    timestamps()
+  end
+
+  @doc false
+  def changeset(context_note, attrs) do
+    context_note
+    |> cast(attrs, [])
+    |> validate_required([])
+  end
+end