Add Voila screengrabber

[treyharris]

This application is unusual: it comes in an dmg containing the naked
app rather than a package, but yet it insists on being run directly
from its install location--no symlinks.

I wasn't able to find another example of such a thing in an existing
cask, so I made a stab at doing it manually.

I just checked and it will work via a Mac alias file, but I don't
know how to create one of those short of calling osascript.

[rolandwalker]

See related comments in #6001.

Two small points about this Cask specifically:

• having the uninstall stanza available for non-pkg Casks is a quasi-undocumented new feature which is supposed to be made official in a few days. It will silently fail for users of older versions.
  • ditto will work better than cp

I'm not opposed to hackery inside the Casks. One might say that this entire project is a hack to hide various install details behind a single interface.

So, if you are impatient with the outlook in #6001, my opinion is that we can merge this on the basis that it "works for now". However,

• I'd prefer to pause until the official waiting period is over (8 Sep) as you have used a new feature.
• If any of the other maintainers object to the complexity, I'd be inclined to defer to their veto.

Many thanks for your contributions to this project.

[vitorgalvao]

This is so old, the cask format is not even this one, anymore, and other things needs updating as well. If you’re still interested in adding, please resubmit, @treyharris.