Dependency between ClockManager and Clocks #88

Hi,

Clock objects contain a reference to a ClockManager. The only usage of this reference is
the invocation of the onClock method on the ClockManager. Is there a reason to not replace
the ClockManager by a ClockListener ?
With this abstraction we could build adapters/wrappers around an existing Clock class (for testing for instance).

Another enhancement could be to replace the use of a Clock class by an instance. That could allows to have parametrized clocks.