Cleaned up the UI for the redirect login.

* The non-JS case is unchanged save not mentioning JS in the message.
* The JS case never shows the form and uses a spinner and a message
  instead. It also delays a bit so the user has a chance to read
  the message and to generally be less jarring.

Change-Id: I86ec05fb6cd8249e7124e176e6f4f44ce8594574
Merge "Cleaned up the UI for the redirect login."