Pascal Precht 113ddc7ce3 feat(ui/shared): allow ModalPopup to receive header components
Similar to its `footer` content, ModalPopup can now receive header components
allowing consumers to design the header part of the modal to their likings.

Usage:

```
ModalPopup {
    id: popup

    header: Item {
			...
		}
	  ...
}
```

The header section will take the height of the root element of the substree
passed to `header`
2020-06-09 17:57:30 -04:00
..
2020-06-09 11:49:23 -04:00
2020-05-28 09:29:17 -04:00