Fix assetpath for nuxeo-user-group-management

The assetpath for nuxeo-user-group-management on the vulcanized version of Web UI is bower_components/nuxeo-ui-elements/, which requires view and edit layouts for users and groups to be placed under ui/bower_components/nuxeo-ui-elements/nuxeo-user-group-management instead of ui/nuxeo-user-group-management, which is where they are expected to be. Consequently, we have those layouts duplicated and it is not clear what files must be overridden in order to contribute custom layouts. This can be done during the build process of Web UI.