Added SPARQL optimizations

* IN is optimized to remove items of its right hand side vector
  that are in conflict with rvr of left hand argument
* If a null variable has no external/global origin, no GSPO uses
  and a single OPTIONAL subvalue then that OPTIONAL becomes plain
  group pattern
* scalar in (scalar1, scalar2, ..., scalarN) is now handled separately
  from say graph-scalar in (vector-of-authorized-graph-IRIs)
Merge branch 'develop/6' into develop/7