Feature/virtualproperty (#286)

* Add virtual property owner to OpenSpaceEngine

* Ability to add and remove virtual properties

* Do not try to render empty PropertyOwner name
Compile fix for iswaComponent
Add example in default.scene

* Delete virtual properties also in the OpenSpaceEngine dtor

* Make RenderablePlanet not crash if the nighttextures are not present

* - Add VirtualPropertyManager to manage ownership of virtual properties
- Only execute regex when it was necessary
-

src/query/query.cpp

@@ -25,6 +25,7 @@
 #include <openspace/query/query.h>
 
 #include <openspace/engine/openspaceengine.h>
+#include <openspace/engine/virtualpropertymanager.h>
 #include <openspace/interaction/interactionhandler.h>
 #include <openspace/rendering/renderengine.h>
 #include <openspace/rendering/renderable.h>
@@ -108,6 +109,15 @@ std::vector<properties::Property*> allProperties() {
         p.end()
     );
 
+    std::vector<properties::Property*> q =
+        OsEng.virtualPropertyManager().propertiesRecursive();
+
+    properties.insert(
+        properties.end(),
+        q.begin(),
+        q.end()
+    );
+
     const Scene* graph = sceneGraph();
     std::vector<SceneGraphNode*> nodes = graph->allSceneGraphNodes();