nongnu: Add zoom.

Here is a package definition for Zoom, did some quick tests and it works. It is possible this not the minimal inputs/wrapping needed, but it does the trick.

Some inspiration was taken from https://github.com/johnlepikhin/guix-channel/blob/master/johnlepikhin/packages/zoom.scm so I added a copyright line for them, though the final package is quite different.

I'll hold for any comments before pushing; I don't have a very full description but otherwise should be fine.