Add ICAO code and utf-8 encoded airport names

Hi!

I used this file in a private project, and noticed that the names of airports seemed to be set to null for airports with special characters in the name. As I needed that, I scraped wikipedia for names and ICAO codes and merged the results with airports.json based on the IATA code. Thus this pull-request contains updated utf-8 encoded names and added ICAO-codes for the airports with IATA-codes that I found on wikipedia.