Refactoring of QueryPlan construction

Moved all QueryPlan producers into an object - QueryPlanProducer
Merge pull request #2383 from systay/queryplanproducer

Refactoring of QueryPlan construction
Update AggregationAcceptance test to not use START
Merge pull request #2385 from systay/aggregation-acceptance

Update AggregationAcceptance test to not use START
Fix availableSymbols in Projection
Add grouping key to QueryGraph and enabling it in QueryGraphBuilder
Introduce aggregation step for planning
Enable aggregation support in ronja
Replace NameSupport with PrefixNameGenerator
Use AggregationNameGenarator in isolateAggregation rewriter

o add an extra test
Remove AggregationAliaser since it is not need due to the use of the isolateAggregation ast rewriter