Disable move to previous slide

[Mauker1]

Sometimes it might be useful to disable the "back" function on the intro screen, so once the user have already finished with one slide he won't be able to come back.

As a suggestion, this could be done like on the original lib:

/* Add a navigation policy to define when users can go forward/backward */
        setNavigationPolicy(new NavigationPolicy() {
            @Override
            public boolean canGoForward(int position) {
                return true;
            }

            @Override
            public boolean canGoBackward(int position) {
                return false;
            }
        });

[bezmian]

It sounds like a good idea. Maybe in future I will implement it.