Added logic to AllHighlights to order featured articles first
Added logic to AllHighlights to order featured articles first

Since we now might have proper article "featured" tag, we can start
ordering it first in the listing. Sadly, base xapian query does not
support this for boolean tags so we do consecutive queries over
query_index to first get all featured articles then append all
non-featured articles.

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib