[ios] better swizzling

This still isn't the "right way" linked in #427, but seems to be safe
and void of side effects due to the namespacing of all the methods.

It has been tested to work side by side with another plugin that also
swizzles AppDelegate's applicationDidBecomeActive.

1. wrapped swizzling in dispatch_once
2. first attempts class_addMethod / class_replaceMethod but if that
fails falls back to method_exchangeImplementations.
3. swizzled_init => pushPluginSwizzledInit (if other plugins attempt to
swizzle init and use the same name, there seems to be a collision)
4. added an observer for UIApplicationDidBecomeActiveNotification
instead of overriding applicationDidBecomeActive
5. applicationDidBecomeActive => pushPluginOnApplicationDidBecomeActive
(and it becomes a notification observer instead)

See http://nshipster.com/method-swizzling/ and "Avoid collisions" under
"Considerations".

This will need testng by someone that understands the plugin better than
I do, but it should not be changing the core functionality at all. The
pushPluginOnApplicationDidBecomeActive method *is* called when the
application becomes active, etc.

Goes a long way toward fixing #427 without regressing #447, etc.

src/ios/AppDelegate+notification.h

@@ -12,7 +12,7 @@
 - (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken;
 - (void)application:(UIApplication *)application didFailToRegisterForRemoteNotificationsWithError:(NSError *)error;
 - (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:( void (^)(UIBackgroundFetchResult))completionHandler;
-- (void)applicationDidBecomeActive:(UIApplication *)application;
+- (void)pushPluginOnApplicationDidBecomeActive:(UIApplication *)application;
 - (void)application:(UIApplication *)application handleActionWithIdentifier:(NSString *)identifier forRemoteNotification:(NSDictionary *)userInfo completionHandler:(void(^)())completionHandler;
 - (id) getCommandInstance:(NSString*)className;
 

src/ios/AppDelegate+notification.m

@@ -23,21 +23,47 @@ - (id) getCommandInstance:(NSString*)className
 // Instead we will use method swizzling. we set this up in the load call.
 + (void)load
 {
-    Method original, swizzled;
-
-    original = class_getInstanceMethod(self, @selector(init));
-    swizzled = class_getInstanceMethod(self, @selector(swizzled_init));
-    method_exchangeImplementations(original, swizzled);
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        Class class = [self class];
+
+        SEL originalSelector = @selector(init);
+        SEL swizzledSelector = @selector(pushPluginSwizzledInit);
+
+        Method original = class_getInstanceMethod(class, originalSelector);
+        Method swizzled = class_getInstanceMethod(class, swizzledSelector);
+
+        BOOL didAddMethod =
+        class_addMethod(class,
+                        originalSelector,
+                        method_getImplementation(swizzled),
+                        method_getTypeEncoding(swizzled));
+
+        if (didAddMethod) {
+            class_replaceMethod(class,
+                                swizzledSelector,
+                                method_getImplementation(original),
+                                method_getTypeEncoding(original));
+        } else {
+            method_exchangeImplementations(original, swizzled);
+        }
+    });
 }
 
-- (AppDelegate *)swizzled_init
+- (AppDelegate *)pushPluginSwizzledInit
 {
-    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(createNotificationChecker:)
-                                                 name:@"UIApplicationDidFinishLaunchingNotification" object:nil];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(createNotificationChecker:)
+                                                 name:UIApplicationDidFinishLaunchingNotification
+                                               object:nil];
+    [[NSNotificationCenter defaultCenter]addObserver:self
+                                            selector:@selector(pushPluginOnApplicationDidBecomeActive:)
+                                                name:UIApplicationDidBecomeActiveNotification
+                                              object:nil];
 
     // This actually calls the original init method over in AppDelegate. Equivilent to calling super
     // on an overrided method, this is not recursive, although it appears that way. neat huh?
-    return [self swizzled_init];
+    return [self pushPluginSwizzledInit];
 }
 
 // This code will be called immediately after application:didFinishLaunchingWithOptions:. We need
@@ -127,10 +153,12 @@ - (BOOL)userHasRemoteNotificationsEnabled {
     }
 }
 
-- (void)applicationDidBecomeActive:(UIApplication *)application {
+- (void)pushPluginOnApplicationDidBecomeActive:(NSNotification *)notification {
 
     NSLog(@"active");
 
+    UIApplication *application = notification.object;
+
     PushPlugin *pushHandler = [self getCommandInstance:@"PushNotification"];
     if (pushHandler.clearBadge) {
         NSLog(@"PushPlugin clearing badge");