Add an API layer for network downloads. Basically QWebnetworkInterface
        is an interface class for downloading resources. QWebnetworkJob describes
        the actual object to download.

        QWebNetworkInterface has a default implementation that replaces the
        old ResourceHandleManager class in the Qt port.

        Remove the ResourceHandleManager class, it is now part of 
        QWebNetworkInterface. Adapt ResourceHandle to the new way 
        of things.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@21619 268f45cc-cd09-0410-ab3c-d52691b4dbfc