mapping tables for CDM-OBS-CORE

[ludwiglierhammer]

Besides the CDM-OBS mapping tables, we can add CDM-OBS-CORE mapping tables.
In the previous GLAMOD releases and the upcomming ones, the data is requested in CDM-OBS-CORE format.

[ludwiglierhammer]

Alternatively, we can implement a function that converts CDM-OBS to CDM-OBS-CORE.