Change country, state, currency lists to CLDR

Change the list of countries, the list of states/provinces from the existing one based on an ISO list 3166-1 (http://www.iso.org/iso/home/standards/country_codes.htm) to a new one based on a UNICODE list (http://cldr.unicode.org/). Other i18n elements should also be reviewed, eg currencies. The benefit is that we would be adopting a standard much more widely used in software, one that D8 is also moving to.

Creating the patch should not be too difficult. As CLDR provides support for the ISO data, that should make it fairly easy to create an upgrade script to change existing values to new ones.

This may be highly important to some people, eg those living in areas/countries that are named differently in the two standards. There will need to be community consultation before doing this change and notice given at time of release including instructions for how to change values back to previous ones.

Background:
CRM-19909 was closed on basis that CiviCRM has been using ISO 3166 standard to determine the countries and states/provinces lists that we include in our tarball. As commented there, there is a competing standard, http://cldr.unicode.org/, that is much more widely used in software including FLOSS projects, including:

Apple (macOS, iOS, watchOS, tvOS, and several applications; Apple Mobile Device Support and iTunes for Windows; …)
Google (Web Search, Chrome, Android, Adwords, Google+, Google Maps, Blogger, Google Analytics, …)
IBM (DB2, Lotus, Websphere, Tivoli, Rational, AIX, i/OS, z/OS,…)
Microsoft (Windows, Windows Phone, Bing, Office, Visual Studio, …)
and many others, including:
Apache, Debian Linux, Eclipse, Free BSD, Gentoo Linux, GroundWork Open Source, GTK+, jQuery, Mozilla, OpenOffice, Mandrake Linux, Perl, Python, QNX, Wikimedia Foundation (Wikipedia)