Allow installation of NPM packages

Howdy! 

I was looking for an ansible way to install node, and since most of them go though the old PPA-- this was the only one that does it the _new_ way. 

Anyway--- I made a few minor changes, a couple yml syntax changes (couldn't run it without those changes). And then created a way to install npm packages as well. I don't know of a way to use items only if a variable exists, so instead I made one with a dummy package name. Ansible will then install everything except that package (if the user doesn't override). 

Also... it isn't up on Ansible galaxy yet. I am _guessing_ that is because this is ... 7 days old? Either way, can you push it? :+1: 

Thanks mate!