Issue/2174 - Show items with no GUI tag in asset in the GUI (#3133)

* Always add GUI properties, even if tag is not in the asset

To make objects wihtout GUI tag be included in the UI

* Hide the hover circle, to clean up scene menu list a little

* set root node gui hidden property to true

* Properly add the gui properties for all scene graph nodes (even root)

* Update GUI hash

include/openspace/scene/scenegraphnode.h

@@ -147,6 +147,7 @@ public:
 
     std::string guiPath() const;
     bool hasGuiHintHidden() const;
+    void setGuiHintHidden(bool value);
 
     static documentation::Documentation Documentation();