Use SolrComponent for Solr index querying and format
response in RDF with Jena.
The ResultSet contains a Pok which himself contains Hits.
If enrichment is activated, all fields presents in index and search
configuration file are annotated.
Component used to :
open a connection to embedded solr server
add a document to the index
search in the index
This class implements singleton pattern in order to share index connection
and improve performance (Solr server is thread-safe).
The index buffer is managed by Solr so we just use a counter to commit
documents when buffer configured size is achieved.