D-Bus: Implement other compound types of properties
* doc/misc/dbus.texi (Errors and Events):
* etc/NEWS: Mention dbus-show-dbus-errors.
* lisp/net/dbus.el (dbus-compound-types): New defconst.
(dbus): New defgroup.
(dbus-show-dbus-errors): New defcustom.
(dbus-ignore-errors): Use it.
(dbus-set-property): Simplify.
(dbus-property-handler): Implement other compound types of properties.