Request internet permission before connect for iOS (#794)

* Attempt to fix API error 1100
* NSURLSession fake call to exec iOS network settings dialog
* use http://captive.apple.com/generate_204 for requesting internet
permission
* moved MobileUtils to IosController
* replaced callbacks with signal-slots in apiController

client/platforms/ios/ios_controller_wrapper.h

@@ -1,6 +1,8 @@
 #import <NetworkExtension/NetworkExtension.h>
 #import <NetworkExtension/NETunnelProviderSession.h>
 #import <Foundation/Foundation.h>
+#include <UIKit/UIKit.h>
+#include <Security/Security.h>
 
 class IosController;
 
@@ -13,3 +15,11 @@ class IosController;
 - (void)vpnConfigurationDidChange:(NSNotification *)notification;
 
 @end
+
+typedef void (^DocumentPickerClosedCallback)(NSString *path);
+
+@interface DocumentPickerDelegate : NSObject <UIDocumentPickerDelegate>
+
+@property (nonatomic, copy) DocumentPickerClosedCallback documentPickerClosedCallback;
+
+@end