iOS: make QWindow views hidden by default

Qt will tell us when the window should be visible. Showing all
windows by default makes e.g the desktop widget visible as
well, which causes problems with activation of windows.

Change-Id: Ibf2283bc5f009df7ff23126f4dd04ec898141720
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

src/plugins/platforms/ios/qioswindow.mm

@@ -109,6 +109,9 @@
         keyboardType = UIKeyboardTypeDefault;
         returnKeyType = UIReturnKeyDone;
         secureTextEntry = NO;
+
+        if (isQtApplication())
+            self.hidden = YES;
     }
 
     return self;