Kicking the energy at every node: flag compute_stoch_kick

The result of the beam envelope calculation in section 6.2, that is to say the quantum fluctuation ${\left\langle{{\delta }^{2}}\right\rangle}_{quantum}$ is stored at every INTEGRATION_NODE is the flag compute_stoch_kick is true. This is used, if the state RADIATION is true, to track with a stochastic kick.

N.B. compute_stoch_kick is overwritten if one tracks with K%envelope=true in the internal state. This is not a problem if the beam envelope is always tracked on the radiative closed orbit.