Use toolbar registry for the deck button and move it to the right

[brichet]

Checklist

• ran doit lint locally

References

Fixes #17

Code changes

• use the settings to add the deck button to the notebook toolbar
• move the button to the right side of the toolbar

Note

The settings cannot be used for markdown files because the toolbar registry seems to be the same for other file types.

User-facing changes

Button moved on le right of the toolbar.

Backwards-incompatible changes

None

[jtpio]

Looks like a good place to put it 👍

Thanks!