Human-readable script.sh.

* Use a shell function to wrap all that sudo shit.
* Escape '/' only when really needed
* Organize code, document stuff
* Remove python-software properties. It's not installed on my system and
  everything seems to go fine.
* Use /bin/bash instead of /bin/sh.
  Maybe it is not necessary, but at least is coherent with other scripts.
  (Yeah, .sh extension is wrong blablabla.)
* Use official nodejs and npm, without adding a remote ppa
Make build-testing-package simpler.

This script is used only once around the whole source.
It has options unused, and it is not really helpul with those command-line
options..