* Returns the type of the slide Cover, Filter, Info, Form, End
* Returns true if this slide is of the type indicated.
* @param type Cover, Filter, Info, Form, End
* Returns the slide title
* Resturns the slide subtitle
* Returns the slide content title
* Returns true if the slide has a defined background image
* Returns the slide background image
* Return true if we can go to the next slide.
* For example, in case of a slide with mandatory question, we can only go to the next slide when an answer is selected.
* Return true if we can go back to the previous slide.
* For example, we can't go back before the first slide.
* Return true if we can skip the current slide.
* For example, a slide with mandatory answers can't be skipped.
* Returns the back button label
* Returns the next button label