Added command line installer argument "allmodules" to enable code path for installing all modules located on disk

There was an unused but useful code path for installing all the modules located on disk instead of just the white-listed modules that come with Prestashop. This is useful when automating many installations with a set of modules other than the core modules.

I broke the method up into two methods, one for getting the modules on the disk and another for using the white-list.

This change does not change the default behavior of Pretashop in any way.

When running the command line installer:

    php install_cli.php --allmodules --domain=foo.com --db_name=me --db_password=secret ...