Introduce QueryPlan that combines a logical plan together with a query graph
Convert AllNodesScan to use QueryPlan
Convert NodeByLabelScan to use QueryPlan
Convert NodeByIdSeek  to use QueryPlan
Convert *RelationshipByIdSeek  to use QueryPlan
Convert Node*IndexSeek  to use QueryPlan
Convert SingleRow  to use QueryPlan
Convert Selection  to use QueryPlan
Construct leaf plans and selection plans using separate plan construction functions

 This separates query graph build-up from plans without overly burdening tests
Merge pull request #2363 from boggle/spike-externalized-qg

Start of refactoring QG to be external from logical plan