This issue intends to spread the use of Evaluator in search code and includes
1. Provide evaluator name for logging.
2. Add option to evaluators for enabling/disabling logging of better h-values.
3. Add option to evaluators for enabling/disabling counting of evaluations.
4. Notify Evaluators about state transitions (issue724).
5. Rename heuristic to evaluator in variable and function names.
With items 2. and 3., we intend to remove dynamic casts for checking if an
Evaluator is a Heuristic. Without the cast to Heuristic, Evaluator must provide
a name for logging (item 1.). Item 4. will finally replace all variables of type
heuristic with variables of type Evaluator in the search code.