Updated reveal.js version and a little cleanup in preparation for a potential release of the tools

[Christofer Dutz <ch...@c-ware.de>]

Hi all,

today I bumped the reveal.js version to the latest version that works.
I even tried going to reveal.js 4.x, but I think we’ll have to wait for the tooling to work for that.
I tried several options, but all of them failed.

As the changes could potentially affect other modules, I did it as a pull request.
It would be great if you others could check, if this works.
https://github.com/apache/incubator-training/pull/68

I think as soon as that’s merged, we could initiate the first release of the tools.

As soon as that’s done I would like to do the official vote on turning on the all commit bit to allow all Apache committers to commit.

Chris