Don't leak all GUI objects on name ambiguity following rP9 and remove ERROR_GROUP GUI.

Delete CGUI::UpdateObjects and don't recreate the entire object hierarchy by recursing through the existing one each time when inserting one GUI Object.
Change CGUI::AddObject to only insert the one relevant pointer into the map hierarchy, return success value and delete the child upon failed insertion in the caller instead of leaking it.
Defer GUIM_LOAD and UpdateCachedSize recursion until all XML files linked in the page XML file were loaded.
Delete related ERROR_TYPE NameAmbiguity, ObjectNeedsName, and unrelated JSOpenFailed and in consistency with the rest, do the LOGERROR in the scope where the error occurs.
Delete ERROR_TYPE InvalidSetting from rP7145 unused following rP22604, rP22796, ERROR_TYPE OperationNeedsGUIObject from rP7145 unused following rP22641, see also rP22741, refs #128.