add api for themes

lib/philomena_web/controllers/api/json/theme_controller.ex

@@ -0,0 +1,11 @@
+defmodule PhilomenaWeb.Api.Json.ThemeController do
+  use PhilomenaWeb, :controller
+
+  alias PhilomenaWeb.SettingView
+
+  def index(conn, _params) do
+    conn
+    |> put_resp_content_type("application/json")
+    |> send_resp(200, SettingView.theme_paths_json(conn))
+  end
+end

lib/philomena_web/router.ex

@@ -157,6 +157,8 @@ defmodule PhilomenaWeb.Router do
         resources "/posts", Forum.Topic.PostController, only: [:show, :index]
       end
     end
+
+    resources "/themes", ThemeController, only: [:index]
   end
 
   scope "/", PhilomenaWeb do