Add an extra parameter to the PropertiesChanged() signal

Add an extra parameter to the PropertiesChanged() signal

It was pointed out on the mailing list that it would be useful to know
that a given property has changed without conveying its value. Because
without this parameter a true_no_value property could change, however
there is no way for a client-side proxy to know _what_ property it was
(only that some property changed).

With the parameter, however, a client-side proxy can reliably discard
a cached property value.

Also rename the "true_no_value" to "invalidates" as the spec is now
using this language.

Also allow using the annotation in the enclosed interface name.

Also rename the annotation name so it uses Property in its name
instead of Properties. This is to be more consistent with the existing
org.freedesktop.DBus.Method.NoReply annotation which uses Method, not
Methods.

Signed-off-by: David Zeuthen <davidz@redhat.com>