declared some stages as final;
added EveryXthPrinter;
removed logging from CollectorSink;
moved id and logger from AbstractStage to Stage

Merger second version

changed merger's behavior corresponding to the last idea in #65

See merge request !18

changed corresponding test and added multiple signal testing

Merger bug

removed bug #65

See merge request !17

Checkstyle solved

Solved a whole bunch of issues regarding checkstyle. For e.g. renamed interfaces to match I[A-Z0-9].* and abstract classes to match Abstract[A-Z0-9].*

See merge request !16