Follow-up Ica9e5a9284: Actually make visualeditor-hidebetawelcome work

Three 'minor' points:

* You have to declare even hidden preferences. Whoops.
* There's no such thing as an "optionsToken", use "editToken".
* You need to POST action=options API calls.

Ahem.

Change-Id: I9c4358107af7bcfca157bd014de49882914e990c