layout.Card: support lazy loading items

module can optionally be a function.

example:

            items: [{
                module         : () => import('./TableContainer.mjs'),
                reference      : 'table-container',
                tabButtonConfig: {
                    iconCls: 'fa fa-table',
                    route  : 'mainview=table',
                    text   : 'Table'
                }
            }, {
                module         : () => import('./mapboxGl/Container.mjs'),
                tabButtonConfig: {
                    iconCls: 'fa fa-globe-americas',
                    route  : 'mainview=mapboxglmap',
                    text   : 'Mapbox GL Map'
                }
            }]

epic.