add recorded year

[agricolamz]

I've looked through the corpora on the server and found out that there is no year of recording field that is easily can be extracted from the audiofile name.

@anapanifica, Anna Sorokina

[ansorox]

Actually, there is a column with date of recording in the meta.csv file. Did you mean something else?

[agricolamz]

I meant in the final json.