add networking helpers to BITAuthenticator

* NSOperation-based networking
* helpers for URLRequest, operation, getPath:error:

Classes/BITHTTPOperation.h

@@ -0,0 +1,25 @@
+//
+//  BITHTTPOperation.h
+//  HockeySDK
+//
+//  Created by Stephan Diederich on 10.08.13.
+//
+//
+
+#import <Foundation/Foundation.h>
+
+@class BITHTTPOperation;
+typedef void (^BITNetworkCompletionBlock)(BITHTTPOperation* operation, id response, NSError* error);
+
+@interface BITHTTPOperation : NSOperation
+
++ (instancetype) operationWithRequest:(NSURLRequest *) urlRequest;
+
+@property (nonatomic, readonly) NSURLRequest *URLRequest;
+
+- (void) setCompletion:(BITNetworkCompletionBlock) completionBlock;
+
+@property (nonatomic, readonly) NSData *data;
+@property (nonatomic, readonly) NSError *error;
+
+@end