Add CORS headers

Implement versions endpoint

lib/matrix_server_web/controllers/info_controller.ex

@@ -0,0 +1,13 @@
+defmodule MatrixServerWeb.InfoController do
+  use MatrixServerWeb, :controller
+
+  @supported_versions ["r0.6.1"]
+
+  def versions(conn, _params) do
+    data = %{versions: @supported_versions}
+
+    conn
+    |> put_status(200)
+    |> json(data)
+  end
+end