Add facilities for D-Bus interface annotations and use them to mark
the old D-Bus interfaces as deprecated.

* mandos (dbus_interface_annotations): New decorator.
  (DBusObjectWithProperties._is_dbus_property): Removed.  All callers
                                                changed.
  (DBusObjectWithProperties._is_dbus_thing): New; generalized version
                                             of "_is_dbus_property".
  (DBusObjectWithProperties._get_all_dbus_properties): Removed.  All
                                                       callers
                                                       changed.
  (DBusObjectWithProperties._get_all_dbus_things): New; generalized
                                                   version of
                                                   "_get_all_dbus_properties".
  (DBusObjectWithProperties.Introspect): Also add interface
                                         annotation tags.
  (AlternateDBusNamesMetaclass.__new__): Also copy interface
                                         annotations.  Add
                                         "deprecated" annotation on
                                         old interface.
  (ClientDBus._foo): New interface annotation to mark non-compliance
                     with the standard property change signal
                     interface.
  (MandosDBusService): Inherit from DBusObjectWithProperties to get
                       interface annotation support.
  (MandosDBusService._foo): New interface annotation to mark
                            non-compliance with the standard property
                            change signal interface.