Add ability to deploy npm package (tarball)

See also: https://github.com/strongloop/strong-pm/pull/12
This might seem like bike-shedding, but basically, there used to e a `--branch`, we got rid of it, and now there is a `--pkg` (why not `--package`, or perhaps `--pack` because its "a npm pack"?), so deploying a branch and deploying a pack are now asymetrical.

Also, I think the URL format is different... git demands the port in the URL, but its optional for package?