Support thesauri with classification

[nichtich]

Several thesauri (GND, STW, FIV...) include an additional classification to group its concepts. By now Cocoda can only show either the classification or the thesaurus, unless both are combined into one vocabulary. Cocoda should support vocabularies consisting of multiple parts, in particular:

• the vocabulary for concepts
• the classification for hierarchy

Connection between these vocabularies must somehow be encoded in JSKOS.

Open questions: whether and how to join or seperate both in Cocoda. The vocabularies might be merged virtually in cocoda-sdk without large changes in Cocoda interface.

Examples:

• GND classification
• STW
• FIV

[stefandesu]

I think there would need to be certain changes in Cocoda as well. For example, looking at the GND classification, each of the listed elements in that hierarchy has many thousands of children, and Cocoda is currently not at all suited to display that. We would need something like a pagination for subtrees, which I imagine is not that easy to implement, especially if you consider the things "around" it (although we might just need to abandon certain features, like showing a concept in the correct place in the hierarchy).

(By the way, the STW hierarchy seems to be supported already since the Skosmos instance directly supplies the data.)