Add class methods for returning login  URLs.

git-svn-id: svn+ssh://svn.savannah.nongnu.org/gap/trunk@2763 d25b4930-3292-e311-b074-0010c6de5da8
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git-svn-id: svn+ssh://svn.savannah.nongnu.org/gap/trunk@2764 d25b4930-3292-e311-b074-0010c6de5da8