Readable logging: print directly request and response objects

I made some changes to get a more readable output in the console.

# For requests
Instead of printing the UTF8 string resulting from the http body (NSData), the code parses this UTF8 string and build a dictionary containing the query pairs (NSString). 

# For Response
The code tries to get AFNetworkingTaskDidCompleteSerializedResponseKey value of the userInfo object. If it's not present, it gets then the responseObject from the AFURLConnectionOperation. Finally if nothing is returned, it falls back on the previous implementation which is getting the AFURLConnectionOperation's responseString.

Then when those objects are printed in the console, the output is indented and very readable.