improve parsing of thesaurus for keywords in iso-to-mmd

[ferrighi]

In iso-to-mmd we only discriminate between keywords with or without "EARTH SCIENCE" string to assign the GCMDSK or None attributes to mmd:keywords. We can improve on this since some provide a thesaurus name. This is not very consistent since it is often used as title string instead of Anchor, but we can do some parsing of CF standard name/CF/Climate and Forecast, based on experience from harvested records.
This should be easy to implement in the code.