Fix JENA-428, allow passing of authentication information for remote updates using the same srv:serviceContext mechanism supported for queries

This involved refactoring UpdateProcessRemote and UpdateProcessRemoteForm to use a common base class where the config functionality was placed.  There was also some changes to HttpOp required to enable use of credentials on the actual HTTP requests.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1462659 13f79535-47bb-0310-9956-ffa450edef68