Generalization of the 'parallel:' facet to grid, species, ask and
experiment. Chnages in the API of IScope for supporting parallel
operations. Changes in QuadTree and GamaGraph for solving sync problems.
Changes in the step method of agents (now divided in 3 sub-methods:
preStep(), doStep(), postStep()). Addition of the
msi.gama.runtime.concurrent package and several classes dedicated to
Signed-off-by: AlexisDrogoul <firstname.lastname@example.org>