Refactor Expand + OptionalExpand to use QueryPlan
Refactor Projection (along with Skip, Limit, Sort, SortedLimit)  to use QueryPlan
Refactor Join  to use QueryPlan
Refactor CartesianProduct  to use QueryPlan
Refactor Optional  to use QueryPlan
Refactor remaining Apply variants and OuterHashJoin to use QueryPlan
Add Visitor support for Query{Plan, Graph} and removed coveredIds from LogicalPlanStringVisitor
Remove coveredIds from LogicalPlan
Remove solved from LogicalPlan
Merge pull request #2370 from boggle/externalized-qg

Externalized qg