Vocab widget: Read default solr, sissvoc locations from CodeIgniter config
when available, otherwise default to hard coded data.
Vocab widget: Added a new (hidden) feature: solr count query injector.

By default, search/narrow items will include a count of solr documents
whose subject_vocab_uri field matches the item's 'about' URI.

This new feature (accessed by options 'sqc', and 'sqc_op') let the savvy
developer inject their own solr query to determine the count.

'sqc' (Solr query count) is the solr query string; 'sqc_op' is the operator
that will join the user's query fragment to the widget's default (vocab uri)
query.

Ideally, sqc_op would always be 'AND', but I'm leaving it open... this does
introduce the risk of specially crafted Solr query URLs that could impact
performance. This risk has been mitigated by... not documenting the option :/