Refactor UrlRequest/UrlProtocol in the Service Kit

 * Remove the BUrlRequest class, which was only delegating work to
BUrlProtocol and subclasses
 * Rename BUrlProtocol to BUrlRequest, and BUrlRequestHttp to BHttpRequest
 * Creating a request is now done through the BUrlProtocolRoster. For
now there is just a static MakeRequest method, this will be completed
when we get to actually allowing add-ons to provide different request
handlers.

This allows cleanup of the API for requests:
 * Remove the universal SetOption method with constants, and have
dedicated setters for each protocol option.
 * Setters can now have multiple parameters, for example you can give
BHTTPRequest a BDataIO and a known size
 * In this case, the BHttpRequest will not use HTTP chunked transfers,
which were always used before and made most servers unhappy (tested and
failed with lighttpd, google accounts and github).