This plugin disables posting for accounts that do not have a
validated email address.
Example:
addPlugin('RequireValidatedEmail');
If you don't want to apply the validationr equirement to existing
accounts, you can specify a cutoff date to grandfather in users
registered prior to that timestamp.
addPlugin('RequireValidatedEmail',
array('grandfatherCutoff' => 'Dec 7, 2009');
Todo:
* make email field required on registration form
* add a more visible indicator that validation is still outstanding
* localization for UI strings
* test with XMPP, API posting
