Lattice and Traceback building

[SimBe195]

This PR adds a class LatticeTrace which is a Tracebackitem together with predecessor and sibling references in order to store the network of trace nodes making up a search lattice. This class is equipped with functions performTraceback and buildWordLattice which trace backwards from the node itself to build up a Traceback vector or StandardWordLattice. This class is going to be used in future search algorithms (e.g. #101).

Note: The Trace class of the AdvancedTreeSearch module is very similar but has a few additional members specific to that module. Because of the self-referential nature of the class (through predecessor and sibling) it is not straightforward to have the AdvancedTreeSearch Trace inherit from LatticeTrace though without introducing a bunch of dynamic_cast calls. So the options are:

• Keep Trace and LatticeTrace separate and accept that they are very similar
• Add the missing members from Trace to LatticeTrace to join them into one single class even though the other members are generally unused
• Make Trace inherit from LatticeTrace and use dynamic_cast wherever siblings or predecessors are accessed