Qt: Remove duplicate GeoIP columns.

Different GeoIP databases have the same column name, e.g. "City"
currently matches two revisions each for IPv4 and IPv6. Map each
uniquely named column to a list of databases and populate
EndpointTreeWidgetItem columns based on the first database match.

Fix a copy/pasteo introduced in g30f3d52: Make sure
geoip_db_lookup_ipv[46] returns longitude instead of latitude.

Change-Id: Idd31f976dfd1cb011cfa7b5aec14b7031ee0e25e
Reviewed-on: https://code.wireshark.org/review/4157
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>