slt-release-finish,start: gitflow release tools

These tools implement the gitflow release process, auto-generating the
changelog and setting the npm package version.

/to @rmg @bajtos 

I needed to cut a strong-supervisor release that was not from the head of origin/master, unsupported by hubflow, so I finally replaced it with a few lines of shell scripts, as threatened.
> I can add npm publish. Do you really want to publish without doing at least a manual check on what is getting published?

What kind of check do you have in mind? I use to run `npm test`.

> Why do you test AFTER running the release tool? 
Shouldn't you test before doing the release? If the test fails, you are in trouble, you'll have a fair amount of manual git work to reset your production branch, and if the origin was updated, to force-push your local branches to the server.

You are right, the test should be done before doing the release. Either at the end of `slt-release-start`, or manually before running the release tool.