marble: Update Czech Republic to Czechia

This year the country has oficially adopted the short name Czechia.
The short name has been entered to the UNTERM and UNGEGN databases in July 2016.
Czechia is used in iso_3166 since September 2016.

Update the CIA/World Factbook country description to the current version mentioning the short name.
Also update the flag description.
The remaining occurences of the political name have been updated with tha last update from geonames.org

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