Email verification and forgot password verification tokens should expire

[Christopher Allan Webber]

Email verification should expire after 30 days and forgot password
verification should expire after 7.

Things that should be done:


-  These fields should be added but not required
-  Views should be modified to add these expiration fields when
   adding the tokens
-  Views should be modified to check the expiration fields before
   using
-  A migration should be added...
   
   -  fields without verification keys should just have the
      email\_verification\_expires and/or fp\_verification\_expires set
      to None
   -  fields with verification keys should set them to a timedelta
      from today


You can set these fields via a timedelta:

::

    >>> import datetime
    >>> datetime.datetime.now() + datetime.timedelta(days=10)
    datetime.datetime(2011, 7, 4, 8, 41, 8, 502139)