Allow clicking the individual steps in multistep forms

[pwkip]

Currently multistep forms force the user to follow all the steps in the predefined order. in over 99% of cases this makes a lot of sense. But it should at least be possible to click the steps and move to a previous step.

In a later phase, we should also allow moving to any step, triggering validation of all the in-between steps in the process, and pausing on the first step that doesn't pass validation.

For now it is possible to add your own custom events to move to a specific step already, but it requires some advanced javascript skills to make this work. https://conditional-fields-cf7.bdwm.be/multistep-example-move-to-specific-step-programatically/