Remove unnecessary trait
Introduce CostModel and some refactoring of logical planning

* Move cost, cardinality and covered ids from LogicalPlan to PlanTableEntry.
These properties are only interesting while planning, not once the plan is finished

* Use costs and not only cardinality for picking plans
Merge remote-tracking branch 'andres/more-logical-plans'

Conflicts:
	community/cypher/cypher-compiler-2.1/src/main/scala/org/neo4j/cypher/internal/compiler/v2_1/planner/logical/IndexLeafPlanner.scala