UX: Rename last "Add variant" form button to "Create variant"

When adding a new variant (Panel), the form submit button on the last step titles "Add variant". That's highly confusing, because when you start by clicking on "Add variant", there's a tab "Add variant", and everywhere else where that string appears, it always means to add a new - not to store/save what you just set up. I'd simply rename that to "Create".