Make 'next' button text customizable in Mentoring Steps.

[Kelketek]

@itsjeyd Ready for your review.

You should be able to test this by:

1. Adding 'step-builder' to the advanced modules.
2. Creating a step-builder block.
3. Adding a Mentoring step block to the step-builder block
4. Adding a question and review to the Mentoring step block
5. Editing the mentoring step block to change the next button label text.
6. Publishing
7. Trying the step in the LMS to see if the next button has your customized text

Heads up @e-kolpakov , this should be coming down the pipe soon, and needs to be included in the release.

[itsjeyd]

@Kelketek When testing your changes I found that if there are multiple Mentoring Step blocks, setting different "Next step" labels doesn't work the way it's supposed to: The label doesn't change from step to step; it's always set to the next-button-label of the first step on the page.

One way of addressing this would be to add a function to MentoringStepBlock (in step.js) that returns the label of the current step, something like:

        getStepLabel: function() {
            return $('.sb-step', element).data('next-button-label');
        }

... and then update via:

        var step = steps[activeStep];
        nextDOM.attr('value', step.getStepLabel());

Also, I think you'll need to update the label not just from updateDisplay but also from jumpToReview (this is called from reviewNextStep, which acts as a click handler for nextDOM while reviewing individual steps). To test this (I didn't), set max_attempts and extended_feedback on the Step Builder block and complete the block in the LMS until you have no attempts left, then use one of the links to jump back to a specific question/step.

[itsjeyd]

@Kelketek Nit: I think it would be good to rename this to something a little less generic, like updateNextLabel or even updateNextButtonLabel.

[itsjeyd]

@Kelketek Looks good, 👍 once the tests pass.