PersistentHTTPClient

Continuing [that](https://github.com/appcelerator/titanium_mobile/pull/2536#issuecomment-8071920) pull request, here is a new  implementation for it.
As i explained in the other pull request, i cant do that in a module as i cant subclass anything but view and proxy.

Also i cant provide an address for testing as the one is authenticated. I am really sorry about that. I have been looking for a test one but couldnt find anything yet.
I am heavily using the ios implementation.