world: show state & country for duplicate city names

In the World tab, for each city, only the city name is shown. This could be confusing since there many cities with duplicate names (e.g. Portland Oregon, and Portland Maine; both in the US but in different states). I have fixed this by displaying the state (if available) and country name for each added city if there's another city with the same name in the list.

NOTE

Deja Vu? It's because this PR is basically this one. I archived my original fork forgetting that that the PR was still open, so here we are.

Due to the fact that my new fork was more up to date, I also fixed the merge conflict caused by this commit, so everything should be good for a clean merge.

Screenshots

Four Londons:

One London, one El Paso, and two Parises:

Fixes: #75