Add HTTP state change event

src/index.js

       }
     })
 
+    let stateEvent = emitter.addListener('RNFetchBlobState', (e) => {
+      if(e.taskId === taskId && promise.onUploadProgress) {
+        promise.onStateChange(e)
+      }
+    })
+
     let req = RNFetchBlob[nativeMethodName]
     req(options, taskId, method, url, headers || {}, body, (err, data) => {
 
       // task done, remove event listener
       subscription.remove()
       subscriptionUpload.remove()
+      stateEvent.remove()
       if(err)
         reject(new Error(err, data))
       else {

src/ios/RNFetchBlobConst.h

 extern NSString *const MSG_EVENT_LOG;
 extern NSString *const MSG_EVENT_WARN;
 extern NSString *const MSG_EVENT_ERROR;
+extern NSString *const EVENT_STATE_CHANGE;
 
 extern NSString *const FILE_PREFIX;
 extern NSString *const ASSET_PREFIX;

src/ios/RNFetchBlobConst.m

 extern NSString *const CONFIG_TRUSTY = @"trusty";
 extern NSString *const CONFIG_INDICATOR = @"indicator";
 
-
+extern NSString *const EVENT_STATE_CHANGE = @"RNFetchBlobState";
 extern NSString *const MSG_EVENT = @"RNFetchBlobMessage";
 extern NSString *const MSG_EVENT_LOG = @"log";
 extern NSString *const MSG_EVENT_WARN = @"warn";

src/ios/RNFetchBlobNetwork.m

 - (void) URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
 {
     expectedBytes = [response expectedContentLength];
+ 
+    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
+    if ([response respondsToSelector:@selector(allHeaderFields)])
+    {
+        NSDictionary *headers = [httpResponse allHeaderFields];
+        [self.bridge.eventDispatcher
+         sendDeviceEventWithName: EVENT_STATE_CHANGE
+         body:@{
+                @"taskId": taskId,
+                @"state": @"2",
+                @"headers": headers
+            }
+         ];
+    }
     
     if(respFile == YES)
     {