Reimplement 9.67-like xauth login flow

Author: theacrat

LegacyLogin/BHTLegacyLoginViewController.h

@@ -0,0 +1,8 @@
+#import <UIKit/UIKit.h>
+
+// Reimplementation of 9.67's built-in xAuth login form for 11.99.
+@interface BHTLegacyLoginViewController : UIViewController
++ (void)presentLoginFrom:(UIViewController *)presenter;
+
++ (UINavigationController *)loginRootNavigationController;
+@end