Add "multi-national" as a country in statistic methodology

[jurecuhalev]

The location field should not be used for displaying the "area of application" of the policy. In most cases this will be no problem. A state policy of Colorado will receive its geolocation in Colorado. Also its "area of application" will be in Colorado. So there is no problem. But we expect issues to appear for multinational policies. The UNESCO Recommendation is located in Paris, France, since this is the location of UNESCO HQ. It`s "area of application" is global. Nevertheless in the statistics it will counted to France at the moment. We agreed, that this Issue should not be solved by the location field. A solution could be to separate all policies which carry the level "multinational" and do not count them to the country of its location. This has to be adressed within a separate issue.
(src: #1975 (comment))

I propose that we add another country called 'Multi-national' and count those repositories and count those policies in there.