Add link instance detection

Signed-off-by: Yihe Li <winmikedows@hotmail.com>

launcher/InstanceDirUpdate.h

@@ -40,4 +40,7 @@
 #include "BaseInstance.h"
 
 /// Update instanceRoot to make it sync with name/id; return true if a refresh is needed
-bool askToUpdateInstanceDirName(SettingsObjectPtr globalSettings, InstancePtr instance, QWidget* parent);
+bool askToUpdateInstanceDirName(InstancePtr instance, QWidget* parent);
+
+/// Check if there are linked instances, and display a warning; return true if the operation should proceed
+bool checkLinkedInstances(const QString& id, QWidget* parent);