nodeview: implemented moving with either the hand tool or middle mouse button

Includes splitting off this functionality from TimelineViewBase so it can be
re-used in any QGraphicsView.

app/widget/nodeview/nodeview.cpp

@@ -26,10 +26,12 @@
 #include "nodeviewundo.h"
 #include "node/factory.h"
 
+#define super HandMovableView
+
 OLIVE_NAMESPACE_ENTER
 
 NodeView::NodeView(QWidget *parent) :
-  QGraphicsView(parent),
+  HandMovableView(parent),
   graph_(nullptr),
   attached_item_(nullptr),
   drop_edge_(nullptr)
@@ -196,7 +198,7 @@ void NodeView::ItemsChanged()
 
 void NodeView::keyPressEvent(QKeyEvent *event)
 {
-  QGraphicsView::keyPressEvent(event);
+  super::keyPressEvent(event);
 
   if (event->key() == Qt::Key_Escape && attached_item_) {
     DetachItemFromCursor();
@@ -209,6 +211,8 @@ void NodeView::keyPressEvent(QKeyEvent *event)
 
 void NodeView::mousePressEvent(QMouseEvent *event)
 {
+  if (HandPress(event)) return;
+
   if (attached_item_) {
     Node* dropping_node = attached_item_->GetNode();
 
@@ -233,12 +237,14 @@ void NodeView::mousePressEvent(QMouseEvent *event)
     drop_edge_ = nullptr;
   }
 
-  QGraphicsView::mousePressEvent(event);
+  super::mousePressEvent(event);
 }
 
 void NodeView::mouseMoveEvent(QMouseEvent *event)
 {
-  QGraphicsView::mouseMoveEvent(event);
+  if (HandMove(event)) return;
+
+  super::mouseMoveEvent(event);
 
   if (attached_item_) {
     attached_item_->setPos(mapToScene(event->pos()));
@@ -296,6 +302,13 @@ void NodeView::mouseMoveEvent(QMouseEvent *event)
   }
 }
 
+void NodeView::mouseReleaseEvent(QMouseEvent *event)
+{
+  if (HandRelease(event)) return;
+
+  super::mouseReleaseEvent(event);
+}
+
 void NodeView::wheelEvent(QWheelEvent *event)
 {
   if (event->modifiers() & Qt::ControlModifier) {