1、为图层添加渲染器和读取器，分离图层基础信息、渲染和读写；

2、LayerTreeLayerNode持有MapLayer图层引用，为右键菜单做准备；
3、改名：imageviewer → mapcavas，mapcavas持有MapLayer图层引用，为刷新图像做准备；

HPPA/LayerTreeLayerNode.cpp

@@ -4,3 +4,19 @@ LayerTreeLayerNode::LayerTreeLayerNode(MapLayer* layer, QObject* parent)
     : LayerTreeNode(layer ? layer->name() : QString(), parent), m_layer(layer)
 {
 }
+
+LayerTreeNode::Type LayerTreeLayerNode::type() const
+{ 
+    return Type::Layer; 
+}
+
+// <20><><EFBFBD><EFBFBD>һ<EFBFBD><D2BB> MapLayer ָ<>루<EFBFBD><EBA3A8>ӵ<EFBFBD>У<EFBFBD>
+void LayerTreeLayerNode::setMapLayer(MapLayer* layer) 
+{ 
+    m_layer = layer; 
+}
+
+MapLayer* LayerTreeLayerNode::mapLayer() const 
+{ 
+    return m_layer; 
+}