add json data export

lib/memex_web/controllers/export_controller.ex

@@ -0,0 +1,17 @@
+defmodule MemexWeb.ExportController do
+  use MemexWeb, :controller
+  alias Memex.{Contexts, Notes, Pipelines, Pipelines.Steps}
+
+  def export(%{assigns: %{current_user: current_user}} = conn, %{"mode" => "json"}) do
+    pipelines =
+      Pipelines.list_pipelines(current_user)
+      |> Enum.map(fn pipeline -> Steps.preload_steps(pipeline, current_user) end)
+
+    json(conn, %{
+      user: current_user,
+      notes: Notes.list_notes(current_user),
+      contexts: Contexts.list_contexts(current_user),
+      pipelines: pipelines
+    })
+  end
+end