[client][actions] Revert an input element with csrf_token.

Without this element, Django (CsrfViewMiddleware) doesn't always
sent a CSRF cookie (It seems to sent for the first access
from a client). However, this causes the troubles.
E.g.)
- When multiple web browsers are used in one computer, the send
  one doesn't get a CSRF cookie.
- After a CSRF cookie expires or when a CSRF cookie is deleted
  manually, a browser may not get a cookie immediately.