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Conflicts:
	src/org/graphstream/boids/BoidSpecies.java
	src/org/graphstream/boids/DemographicManager.java

It is actually created with a constant probability of 0.01 for birth and
death for each species.

A bug remains : a species disappear, is this tied to the display and
ui.class ??

Fix setForcesFactory() and add an init() method to BoidForcesFactory called one time by BoidGraph when forces factory is set.

They are not yet connected to the main simulation code.

Add a new parameter to add a value in the 'ui.class' attribute of boid nodes to allow a by-species custom css.