adds base class Displayable. Any class which is supposed to be
drawn/displayed on the screen should be extending this class. This way
we can always say: which classes can be "displayble" on the screen, and
which are performing some other purpose.
Fixes it to use new version of Timer constructor (decoupled from
MatchIt.java)
changes Timer so that it doesn't depend on MatchIt anymore. This is done
by decoupling Timer from millis() method. But the price we pay for this
decoupling is that we had to switch to long type for the time types.
This has triggered a cascade of changes in different classes.