Add belaqi_anmean value to index wheel

[opeeters]

On both the landing and the info tab, the second "Fairly good" in this case should be the result of the belaqi_anmean_2019 layer we published today. We were not able to implement this yet due to the absence of the relevant annual mean layer. The big "Fairly good" should still come from belaqi_hmean, the small one from the most recent belaqi_anmean (cf "lastupdate_year" in https://www.irceline.be/air/time_app_json.php).

[janschulte]

Done with commit https://github.com/irceline/aq-mobile-be/commit/44db83d95a7d3da688c4d46c87806c006cfc32f2

[opeeters]

Thanks everyone!