Extend list of vocabularies at front page

[nichtich]

The current plain list of vocabularies, optionally grouped in flat categories should be extended. This needs some brainstorming on existing ideas and requirements mentioned in discussion before such as:

• sub-categories
• grouping of multiple editions of a vocablary
• facets to show/hide vocabularies with selected properties (e.g. by language, type, subject...)
• include more metadata information about each vocabulary (description, keywords, term count...), possibly configurable via templates

The list of vocabularies at front page should be customizable for both instances with a small number of vocabularies and instances with many vocabularies.

[hekl]

For these functions there is support in the XKOS standard. Otherwise some Dublin core terms could be useful too: dct:isVersionOf, :hasVersion, :isPartOf, :hasPart, :isReplacedBy, :replaces.

• one issue is then putting vocabularies in categories, using this in the front-end and configuring this in the backend as relations or shared configurations;
• second: relating vocabularies to each other in the case of editions or versions, yearly or otherwise, There should of course be a a way to show this in the front end.