Implement total spin conservation rule

[ptalou]

**Is your feature request related to a problem?

In a fission reaction, the spins of the fragments follow the conservation rule: J_1+J_2+l=J, where J_1,2 are the fragment spins, l the orbital angular momentum, and J the total spin of the compound fissioning parent nucleus. In the current version of CGMF, no constraint is applied to the values of l.

Describe the solution you'd like

Limiting the values of the orbital angular momentum l would create a correlation between the fragment spins. Studying the impact of this reasonable assumption on gamma data, in particular, would be interesting.