Based on how new tours are defined with non-linear transitions (NLT)
Looked at how lib.Step has transitions. Can assign transition/next. Have a back callback, with same functionality as back.
Can we use .back() analogously to .next()?
This part is okay
Start with .back() and maybe revisit later.
.shouldShowBack()
Interimly, if back only sometimes would work on particular step, don't include it.
No shouldShowBack() for now
If .back() is called, show the back button.
Do the same thing for .next(), but accept action: 'next' (deprecated) for backwards compatibility. If action: 'next' is not specified, generate the next button.
No action: 'back'
No auto-wiring for now (generating back button if there was previously a next)