[TIMOB-10835] TiAPI: HTTPClient: new event for continuous data stream

Feature description

HTTPClientProxy should support didReceiveData method.

Customer's original description of the request

I needed to have a comet session using Titanium on iOS. Right now the implementation of TiNetworkHTTPClientProxy doesnt allow this because it doesnt implement didReceiveData of ASIHTTPRequest. Though using didReceiveData would have broken ondatastream and onsendstream. So what i did was create a third one "ondatastream" for live data processing. In the meantime i renamed(for now) ondatastream to ondownloadprogress and onsendstream to onsendprogress. WARNING: on ios using the new "ondatastream" will break responseText and responseData. This is due to the ASIHTTPRequest implementation

Pull request

See https://github.com/appcelerator/titanium_mobile/pull/2844 and related links and discussions.