synchronized critical part in LabelingMapping
DoG: javadoc to explain threshold normalization and param to turn it off.
Merge branch 'master' into gauss-executionservice
DoG: Instead of passing ExecutorService to getPeaks(), it can be set on
the DogDection object. If it is set to null, a new ExecutorService
according to numThreads is created.

This is not the final solution.