Removed arithmetic targets map by extending Target class to also contain a Node. Made preliminary work for moving the "do we need to add the successors to the worklist"-check to the worklist algorithm.
Renamed Target.constant to Target.fixpointReached.
Changed worklist algorithm in FirmOptimizer to check if a node changed and add the successors in that case.
Splitted optimization visitors in multiple files.
Changed visitor replacement from Target to Node.
Changed Visitor calling to Factory-Pattern.
Fixed topological graph traversing in FirmOptimizer.
Removed branch exclude for travis.