Request: Allow CMS to be embedded in a UI

**Is your feature request related to a problem? Please describe.**
We are looking to add a header above the CMS containing some branding and info about which branch the CMS is currently editing.

Currently it is possible to edit the `index.html` and use a container with the id `nc-root` to control where the cms is loaded, however due to the architecture and styles used in the CMS (they use 'position: static`) it is impossible to define any UI above or below the CMS as it will be immediately obscured by the CMS which fills the entire body.

**Describe the solution you'd like**
It would be great if the CMS respected the bounds of its containing element, or offered some other way to include a header and footer above and below.

**Describe alternatives you've considered**
The only option is to also use `position:static` and overlay any new UI, which looks awful.

**Additional context**