Fix bug where a script execution would stop completely if a property was not found

Added helper file to ease Lua script callback testing
Made errors in setPropertyValue and getPropertyValue functions not fatal

include/openspace/scripting/scriptengine.h

@@ -98,7 +98,7 @@ private:
 	std::vector<std::string> _queuedScripts;
 	std::string _currentSyncedScript;
 };
-  
+
 } // namespace scripting
 } // namespace openspace