Add Conditional navigation to Interactive Book

Hi!

The Interactive Book features an "automatic progress" option described as:

Enable automatic progress
If enabled a page without tasks is considered done when viewed. A page with tasks when all tasks are done. If disabled there will be a button at the bottom of every page for the user to click when done with the page.

I suggest adding a "Conditional navigation" option, similar to the Sequential Navigation method that is available in the Moodle Quiz activity. It would work as described below:

Navigation method Free / Sequential (boolean field)
In Sequential mode, a page without tasks is considered done when viewed (and the end-user is allowed to navigate to the next page). On a page with tasks, the user is only allowed to navigate to the next page when all tasks on that page are done. In Sequential mode the user MUST go through all the pages of a book before being allowed to display the Summary and Submit page.

I hope this makes sense.