Add Vocabulary class

[orviz]

Includes vocabularies for IANA media types and FAIRSharing

[ferag]

Is terms_map now mandatory?
I have also some issues with plugin.metadata_utils. I'm not sure how it should work.

[orviz]

Is terms_map now mandatory? I have also some issues with plugin.metadata_utils. I'm not sure how it should work.

• terms_map should be defined in the plugin's config.ini. It should contain the mappings of the plugin's metadata schema and the ones used internally
• the metadata_utils property has to be defined as a method in the plugin class (probably there is a smarter way to do it). This property returns the class that implements the gather methods of the plugin. So this is again something that is specific to the plugin.