Move "Next" button to the right

[gregorni]

Right now, both the "Back" and the "Next" button are on the left of the header bar. I personally find it more intuitive to have the "Back" button in the top left, and the "Next" button in the top right of the window.

[marcoceppi]

I agree, but was unfamiliar on how to do that. I'll test your PR shortly!