2.4.0-ehri

This release is updated to work with Solr 6.x.

There are additional changes specifically for the EHRI-project:

• the search path has been changed from '/solr-search' to '/search'
• the way facets are encoded in the URL has changed from: ?facet=<solr_field>:<value> to ?f[]=<ElementLabel>:<value>, e.g:

Old: ?facet=50_s:Germany
New: ?f[]=Title:Germany