Add a fix to the window resolution for Retina displays

Add a new setting to the ConfigurationManager that can specify whether to scale the onscreen text by window size or resolution

include/openspace/engine/configurationmanager.h

@@ -97,6 +97,9 @@ public:
     /// The key that stores the time (in seconds) that the application will wait before
     /// shutting down after the shutdown call is made
     static const std::string KeyShutdownCountdown;
+    /// The key that stores whether the onscreen text should be scaled to the window size
+    /// or the window resolution
+    static const std::string KeyOnScreenTextScaling;
     /// The key that stores whether the master node should perform rendering just function
     /// as a pure manager
     static const std::string KeyDisableMasterRendering;