Add site codes in json files

[mifads]

The json files produced by pyaerocom have loads of meta-data, but do not contain the site codes. The Ebas database is the most important one for the EMEP project, and such site codes exist and are widely used. They also indicate the station type with a simple system: G, R or U. In general these codes are much more useful for manipulating data than station names.

So, please add site codes to the json files along with the other meta data. It would be VERY useful.

[charlienegri]

station_type has been added to some of aeroval's json output (the files in the map folder iirc) because of cams2_83, that needed it for the fairmode plots, the logic is such that it is up to each reader to read/add that info and pass it to the ungridded data object, otherwise it will be empty, so far only the cams2_83 reader uses that as far as I am aware
given this, it would be probably better to used that in the case of ebas instead of adding a new metadata field in the ungridded data object (which is a pain)

[mifads]

An alternative would be to store the name of the file from which the data came, e.g. Birkenes II may come from NO0001R.20040101.total_carbon.pm25.1y.1wk. I could quickly grab the code from that, but this is very Ebas specific, and sounds like another metadata field anyway. A very crude option is to have the code-station_name mapping in a table made while processing Ebas. Just for us poor EMEP'ers that might want to output tables with NO0001, NO0002 etc, in alphabetical order ;-)

[jgriesfeller]

This is related to metno/pyaro#90 (we don't have a metadata standard)