Transition delay when launching DemARK notebook

[DrDrij]

I just clicked on a link that I had constructed to launch a DemARK notebook via the https://econ-ark.org/materials API. It worked. But the transition from https://econ-ark.org/materials was so fast that a user might not even notice it. I want there to be enough of a delay that they might process the fact that there is this underlying tool "https://econ-ark.org/" that maybe it would be worth checking out.

So, maybe a 1 second delay before executing the autoforward would be good.

@llorracc Perhaps a small loading animation with the text describing what is going on in the background.

[DrDrij]

Addressed in PR #56