Implement multi-input OFX clip wiring and texture handling

Store PluginJob input values for lookup
Add per-clip texture inputs on plugin nodes
Map input clips to textures during render (with Source fallback)

app/node/node.h

@@ -1303,6 +1303,8 @@ signals:
 
 	void KeyframeTimeChanged(NodeKeyframe *key);
 
+	void MessageCountChanged();
+
 	void KeyframeTypeChanged(NodeKeyframe *key);
 
 	void KeyframeValueChanged(NodeKeyframe *key);