Managing Utility Registrations
------------------------------

The user interface for utility registration management allows us to
deactive a registration by selecting the adjacent checkbox and
clicking "Deactivate"::

  >>> print http(r"""
  ... POST /++etc++site/default/Utilities/utilities.html HTTP/1.1
  ... Authorization: Basic bWdyOm1ncnB3
  ... Content-Length: 85
  ... Content-Type: application/x-www-form-urlencoded
  ... 
  ... selected%3Alist=%3Azope.app.session.interfaces.IClientIdManager&Deactivate=Deactivate""") \
  ... #doctest: +NORMALIZE_WHITESPACE
  HTTP/1.1 200 Ok
  Content-Length: ...
  Content-Type: text/html...
  ...
  <div class="message">
  Deactivated: IClientIdManager, implemented by CookieClientIdManager
  'CookieClientIdManager'
  ...

Once we've deactivated a utility registration, we can remove it by
again checking the checkbox next to it in the list and clicking
"Delete"::

  >>> print http(r"""
  ... POST /++etc++site/default/Utilities/utilities.html HTTP/1.1
  ... Authorization: Basic bWdyOm1ncnB3
  ... Content-Length: 77
  ... Content-Type: application/x-www-form-urlencoded
  ... 
  ... selected%3Alist=%3Azope.app.session.interfaces.IClientIdManager&Delete=Delete""") \
  ... #doctest: +NORMALIZE_WHITESPACE
  HTTP/1.1 200 Ok
  Content-Length: ...
  Content-Type: text/html...
  ...
  <div class="message">
  Deleted: IClientIdManager, implemented by CookieClientIdManager
  'CookieClientIdManager'
  ...
