Merge branch 'develop' into feature/scenegraphloader

Conflicts:
	src/abuffer/abuffer.cpp
	src/rendering/renderengine.cpp
	src/scene/scene.cpp

include/openspace/scene/scenegraphnode.h

@@ -68,6 +68,8 @@ public:
     void addNode(SceneGraphNode* child);
 
     void setParent(SceneGraphNode* parent);
+	bool abandonChild(SceneGraphNode* child);
+
     const psc& position() const;
     psc worldPosition() const;