Feature Request: Gating of next button

[cgalvan]

Might be a good idea to add a feature for gating (disabling) of the Next button on the tutorial until some action is completed. This could be done by providing an optional field on the step that would disable the Next button until some signal is fired from the step. This way, the custom tutorial could write some logic to listen for an event/action and then fire the signal that would re-enable the Next button to allow the user to proceed with the tutorial.