Add support for previous page

[subbu05]

In few cases there is support for going back to revisit last page.

[sensejoy]

You can go back using left arrow key in the first several pages, however it fails afterwards.

[bdsys]

Perhaps add a directory / table of contents?

I wanted to go back and watch the network partitions problem and resolution at the end. However, I was too impatient/lazy to proceed through the entire presentation.

[justinclift]

Definitely agree. The UI definitely needs a "back" button added, probably to the left of the "restart" one. 😄