Update the subpages of Creating Nuxeo Packages

The main page https://doc.nuxeo.com/nxdoc/creating-nuxeo-packages/ has been reviewed for LTS 2017 but its subpages need to be reviewed / updated / cleaned up regarding the latest changes and the current way of building a package and its dependencies.

For instance:

• Package Manifest: not sure the nuxeo-automation example and the package.xml file are relevant.
• Packaging Example: not sure if we still want to suggest the 3 methods.
• Scripting Commands: are they up-to-date? There's even a "TODO" at the bottom of the page.