Adds a child to this.
The child is identified by the name. The title will be used by `GtkStackSwitcher` to represent child
in a tab bar, so it should be short.
| this |
a `GtkStack` |
| child |
the widget to add |
| name |
the name for |
| title |
a human-readable title for |
|
the `GtkStackPage` for |