Removed the unused constructors in GTransport and also modified setting
the headers, url and query parameters in the request() method. This
helps in re-using the mTransport object in GContactClient. Moved
setting the "GData-Version: 3.0" header to the constructor, else, the
data is not being retrieved as per version 3.0. A startIndex counter is
used to keep track of number of requested entries. Using the url in
<link> throws a HTTP 403 error. Modified the signature of parse ()
method to take the xml buffer and return the GAtom object. Moved the
network configuration parameters to GConfig

Signed-off-by: Sateesh Kavuri <sateesh@mobilitas.co>