#5560 use new page shell for consistent shell layout

Page shells are now split into more elements, so there will be more consistency in the pageshell. It also allows for easier override of page body (used in theming where page/default was overridden, but now only page/elements/body/default needs to be overridden).

There is also a small improvement in the default layout as the topbar view now is only executed if there is need for it.