Removed dead code
Replaced constants with ENUMs
Made EventWindow#show() thread safe

Swing is not thread safe and offers
SwingUtilities#invokeLater(Runnable) and
SwingUtilities#invokeAndWait(Runnable) to safely make changes to its
data model.
Do not allow system buttons to close window

Implementing correct state machine termination using #dispose() would
be a better but is too complex.
Proper termination on state machine shutdown