* 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
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