Modified ExcelTimingWriter to handle timings for PISDF actors.
ExcelTimingWriter now loop on vertices names rather than vertices themselves, making it neutral wrt. the kind of SDF graph it processes (IBSDF o PISDF).
Few changes in ExcelWriter (abstract superclass) and PreesmAlgorithmListContentProvider APIs (a new exception possibly thrown and a method went from private to public)
Modified ExcelTimingParser to handle timings for PISDF actors.
ExcelTimingParser now look for vertices names rather than vertices themselves, making it neutral wrt. the kind of SDF graph it processes (IBSDF o PISDF).