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

src/engine/configurationmanager.cpp

@@ -72,6 +72,8 @@ const string ConfigurationManager::KeyDisableMasterRendering = "DisableRendering
 const string ConfigurationManager::KeyDownloadRequestURL = "DownloadRequestURL";
 const string ConfigurationManager::KeyRenderingMethod = "RenderingMethod";
 
+const string ConfigurationManager::KeyOnScreenTextScaling = "OnScreenTextScaling";
+
 const string ConfigurationManager::KeyHttpProxy = "HttpProxy";
 const string ConfigurationManager::PartHttpProxyAddress = "Address";
 const string ConfigurationManager::PartHttpProxyPort = "Port";