Psionic training

anytimePsiTraining option:
 - Any soldier can be placed into (or removed from) psi-training at any time;
 - Initially soldiers will start with a negative psi-skill value which will be used to determine how many more days (30-50) of psi-training they need to unlock their psi-potential;
 - Psi-Training calculated every day at 00:00;
 - Soldiers with psi-skill < 0 would get ++psi-skill each day;
 - Soldiers with psi-skill == 0 would get +14 to +26 psi-skill;
 - Soldiers with psi-skill > 0 have a chance of getting a psi-skill equal to 10/(psi-skill);
 - You can anytime switch back to (or from) vanilla behavior;
 - For return to vanilla behavior: all soldiers need sent to psi-training, switch back option to "No" and wait end of month.