[Image] Add examples to UIExplorer, fix some bugs

Summary:
Add two simple examples.
![image](https://cloud.githubusercontent.com/assets/1004115/8674092/03052652-2a55-11e5-8531-8f01c7970af4.png)

Also:
- do not start the task at DownloadTaskWrapper (it starts from ImageDowloader if image isn't cached yet);
- fire `onLoadAbor`t event;
- send more readable `error.localizedDescription` with `onLoadError`;
- rename `onLoaded` to `onLoadEnd`
Closes https://github.com/facebook/react-native/pull/1987
Github Author: Dmitriy Loktev <unknownliveid@hotmail.com>

Libraries/Image/RCTDownloadTaskWrapper.m

@@ -66,7 +66,6 @@ static void *const RCTDownloadTaskWrapperProgressBlockKey = (void *)&RCTDownload
   task.rct_completionBlock = completionBlock;
   task.rct_progressBlock = progressBlock;
 
-  [task resume];
   return task;
 }
 

Libraries/Image/RCTImageDownloader.m

@@ -110,7 +110,7 @@ CGRect RCTClipRect(CGSize, CGFloat, CGSize, CGFloat, UIViewContentMode);
           runBlocks(NO, response, data, error);
         }
 
-        if (response) {
+        if (response && !error) {
           RCTImageDownloader *strongSelf = weakSelf;
           NSCachedURLResponse *cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:response data:data userInfo:nil storagePolicy:NSURLCacheStorageAllowed];
           [strongSelf->_cache storeCachedResponse:cachedResponse forRequest:request];

Libraries/Image/RCTNetworkImageView.m

@@ -86,6 +86,8 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
 {
   if (![_imageURL isEqual:imageURL] && _downloadToken) {
     [_imageDownloader cancelDownload:_downloadToken];
+    NSDictionary *event = @{ @"target": self.reactTag };
+    [_eventDispatcher sendInputEventWithName:@"loadAbort" body:event];
     _downloadToken = nil;
   }
 
@@ -146,7 +148,7 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
             loadEndHandler();
           });
         } else if (error) {
-          errorHandler([error description]);
+          errorHandler([error localizedDescription]);
         }
       }];
     } else {
@@ -170,7 +172,7 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
             loadEndHandler();
           });
         } else if (error) {
-          errorHandler([error description]);
+          errorHandler([error localizedDescription]);
         }
       }];
     }

Libraries/Image/RCTNetworkImageViewManager.m

@@ -47,7 +47,7 @@ RCT_CUSTOM_VIEW_PROPERTY(tintColor, UIColor, RCTNetworkImageView)
   return @{
     @"loadStart":    @{ @"registrationName": @"onLoadStart" },
     @"loadProgress": @{ @"registrationName": @"onLoadProgress" },
-    @"loaded":       @{ @"registrationName": @"onLoaded" },
+    @"loaded":       @{ @"registrationName": @"onLoadEnd" },
     @"loadError":    @{ @"registrationName": @"onLoadError" },
     @"loadAbort":    @{ @"registrationName": @"onLoadAbort" },
   };