Move voila-reveal to core voila

[SylvainCorlay]

It is confusing to users that without installing voila-reveal, the command voila --template=reveal will work because the reveal template is found in nbconvert. Worse, it will simply fail silently to connect to the kernel because it is not a proper voilà template.

One way to make things better could be to move voila-reveal to core voila.

[SylvainCorlay]

@maartenbreddels what do you think of this proposal?

[maartenbreddels]

Yes, good call. Makes total sense, because reveal is standard in nbconvert as well.

[SylvainCorlay]

Thankfully, voila-reveal already specifies voila<0.3, so that we can add the template to core voilà and set the version to 0.3dev.