Property notifications are queued during object initialization and
reloading, but the added/removed signals were emitted immediately
even before the object was fully initialized.

Additionally, depending on how long asynchronous initialization took,
the notifications could have been emitted before the object was
fully initialized as deferred_notify_cb() wasn't being suppressed
until all the properties were complete.

For synchronous intialization, signals could be emitted at various
times during initialization and not all of the object's properties
may be read.  Furthermore property notifications were queued in an
idle handler, which breaks users that may not use a mainloop.  All
signals and notifications should be emitted immediately after
initialization is complete for synchronous initialization.

To make things consistent and ensure that all signals and notifications
are emitted only when initialization is complete, queue signals for
deferred emission and only run notifications/signals when all the
object's properties have been read.  For synchronous initialization,
emit all notifications and signals immediately after initialization
and not from an idle handler.