Add script to plot timeline as created by TimelineSvc

@leggett, I added a script (hivetimeline.py) to make a nice graphical representation of the timline.cvs file created by the TimlineSvc. This obviously is only useful for small toy examples but it helped me tremendously in understanding what the scheduler actually does. Probably could be useful in our tutorials as well. Here is an example:

There is one band per thread (the script can also plot slots instead of threads but that's less useful) and shows the time in algorithms as well as which event is being processed. On the very top it shows the events in flight.