GEAR: add a new flag : CHIMIE_EJECTA_RADIUS that allows to fix the radius of the ejecta.

CHIMIE_EJECTA_RADIUS=0 : default (sph)
CHIMIE_EJECTA_RADIUS=1 : use tee parameter ChimieEjectaRadius
CHIMIE_EJECTA_RADIUS=2 : not implemented yet but could use a value that

			  depends on local physical quantities