This class is a singleton that specifies which
HTTPRequestService to use. It also uses
DataDroid base class as a proxy to call the Service. It provides easy-to-use methods to call the
service and manages the Intent creation. It also assures that a request will not be sent again if
an exactly identical one is already in progress.
Take care that the 'listener' is referenced until the callback is delivered to the listener. If
the listener is garbage collected, then the listener callback will not execute. For calls to:
void execute(Request request, RequestManager.RequestListener listener) {