This demo shows how different editing operations cause commands to be executed,
the command stack to be filled, command listeners to be notified. The timeline
objects shown support different editing features. The start time of some of them
can be changed, some allow that their duration gets changed and some allow the
user to move them to a different node / row. The command stack list shows which
commands are currently stored on the command stack. The console at the bottom
shows the events being fired by the command stack.
