Add a signal to indicate VCA creation

As opposed to VCAAdded this is not emitted when re-loading a session
and only emitted when a user creates a new VCA.

libs/ardour/ardour/vca_manager.h

@@ -54,6 +54,7 @@ public:
 	VCAList::size_type n_vcas() const { return _vcas.size(); }
 
 	PBD::Signal1<void,VCAList&> VCAAdded;
+	PBD::Signal0<void> VCACreated; /*<< is not emitted during set_state */
 
 	XMLNode& get_state();
 	int set_state (XMLNode const&, int version);

libs/ardour/vca_manager.cc

@@ -111,6 +111,10 @@ VCAManager::create_vca (uint32_t howmany, std::string const & name_template)
 
 	VCAAdded (vcal); /* EMIT SIGNAL */
 
+	if (!vcal.empty ()) {
+		VCACreated (); /* EMIT SIGNAL */
+	}
+
 	_session.set_dirty ();
 
 	return vcal;