Fix javadoc link
Simplify CandidateList by removing pruning
Move covering concept from LogicalPlan to QueryGraph
Renamed Projections to QueryProjection
Introduced the concept of NoProjection
Introduce PlannerQuery

Instead of using QueryGraph to represent a whole
query, this commit now introduces a PlannerQuery,
which has this role. The PlannerQuery contains a
QueryGraph and a QueryProjection, and the WITH
structure of a query.
Break up PlanningStrategy

Now two parts solve CypherQueries together -
QueryGraphSolver solves the actual MATCH part
of a query, and QueryPlanningStrategy handles
projection and WITH.
Add AggregationProjection

This allows a PlannerQuery to represent a query
with aggregation