Multiple changes and improvements to the handling of users:

Multiple changes and improvements to the handling of users:
  User preferences.
    User can change their email address, and it is verified.
    User can change their email notification status.
  Invite user to join is now much less of a hack.
    This option has moved to the front page.
    Don't send email notifications to non-accepting users.
    Administrator can see who has not yet accepted their invitations.
  Delete user works again.
  Stylesheet fixes throughout user management.

In the database:
  Added users.invite
  Added pending_email_changes table.

Updated MANIFEST.