Move static FE routing into its own plug.

Previously it was piggybacking on FallbackRedirectController for users
and OStatusController for notices; now it's all in one place.

lib/pleroma/plugs/static_fe_plug.ex

@@ -0,0 +1,14 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Plugs.StaticFEPlug do
+  def init(options), do: options
+
+  def call(conn, _) do
+    case Pleroma.Config.get([:instance, :static_fe], false) do
+      true -> Pleroma.Web.StaticFE.StaticFEController.call(conn, :show)
+      _ -> conn
+    end
+  end
+end