Implement countries serialization

Countries now show the cumulative traffic since ntopng restart as this is consistent with the other views

scripts/lua/get_country_data.lua

@@ -0,0 +1,27 @@
+--
+-- (C) 2013-19 - ntop.org
+--
+
+dirs = ntop.getDirs()
+package.path = dirs.installdir .. "/scripts/lua/modules/?.lua;" .. package.path
+require "lua_utils"
+require "country_utils"
+local json = require("dkjson")
+
+sendHTTPContentTypeHeader('text/html')
+
+-- sendHTTPHeader('application/json')
+interface.select(ifname)
+
+local country = _GET["country"]
+
+interface.select(ifname)
+
+local country = interface.getCountryInfo(country)
+
+local res = {}
+if country ~= nil then
+   res = country2record(getInterfaceId(ifname), country)
+end
+
+print(json.encode(res, nil))