Added Pragma response header for HTTP 1.0 and added HTTP 1.1 check for Vary response

HTTPTimeSeekResponse.DLNAPlaySpeedResponse.add_response_headers() now add the
 no-cache Pragma header for HTTP 1.0 requests (per DLNA .

The Vary header is now only included for HTTP 1.1 requests.

Logic in the HTTPRequest constructor to set the HTTP version of the response
 is relocated to the end of HTTPGet.handle_item_request().

 The way the libsoup apis work, there's no differentiation between the
 request HTTP version and the response HTTP version. So to allow the
 processing code to tailor its behavior to the HTTP version of the request
 (in accordance with DLNA 7.5.4.3.2.7.3), but unconditionally respond
 as HTTP 1.1 (in accordance with DLNA 7.5.4.3.2.7.2), the version must
 be set at the end of processing.

 This functionally was added via Gnome Bugzilla 702555. So requested
 it be revisited.

Tested with HTTP 1.0 and 1.1 requests with various PlaySpeed and
 TimeSeek headers and confirmed the correct Vary/Pragma headers are
 being added.