Adding constant subject native SPARQL support through jcr/sql2 conversion.

https://www.pivotaltracker.com/s/projects/684825/stories/71322140

The following SPARQL with constant subject pattern supported: 
PREFIX fcrepo: <http://fedora.info/definitions/v4/repository#>
select ?date where { <http://localhost:8080/rest/foo> fcrepo:created ?date }

PREFIX fedorarelsext: <http://fedora.info/definitions/v4/rels-ext#> 
select ?part where { <http://localhost:8080/rest/foo> fedorarelsext:hasPart ?part}

PREFIX dc: <http://purl.org/dc/elements/1.1/> 
PREFIX fedorarelsext: <http://fedora.info/definitions/v4/rels-ext#> 
select ?title where { <http://localhost:8080/rest/foo> fedorarelsext:hasPart ?part . ?part  dc:title ?title}