added a ruler for measuring

added support for meta-data editing
improved element selection
changed zooming
fixed some issues with layer events
fixed issue with 3D outline
fixed loading issue for old maps
some interface changes

params/ToolBoxWidget.h

@@ -8,7 +8,9 @@ class QPushButton;
 class MapView2D;
 
 /**
- * gui element with actions to perform
+ * the toolbox on the left of the map.
+ * gui element with actions to perform.
+ * add new elements, etc.
  */
 class ToolBoxWidget : public QWidget {
 
@@ -32,6 +34,7 @@ private:
 	int r = 0;
 
 	QPushButton* btnSelect;
+	QPushButton* btnMeasure;
 
 	QPushButton* btnGround;
 	QPushButton* btnWall;
@@ -49,6 +52,7 @@ private:
 private slots:
 
 	void onSelect();
+	void onMeasure();
 
 	void onNewGround();
 	void onNewWall();