Introduce Selections to the QueryGraph and SQGBuilder

o SQGB: For now only works with HasLabels() in MATCH
o Renamed ProjectionPipe to ProjectionNewPipe
o QueryGraph: Projections are now a Map[String, Expression]
Prototype simple label scan support for new planner
Merge pull request #2096 from boggle/2.1-plan-label-scans

2.1 Label scan support for new planner [DONT MERGE, Waiting for fix on master]