Delta time bugfixes for Dead Air 0.98b addon

These bugfixes fix a number of errors related to incorrect time determination in certain algorithms. There are two such fixes: battery drain and squad respawn. In the first case, everything is simple - devices spend energy at a constant rate, and not at a "random" rate, as it was in the original. In the second case, the "last spawn" variable depends on the amount of "missed frequency", which allows squads to spawn at the right time with the right frequency. In addition, squads will not spawn if the respawn time "jumped", so after waking up, smarts will not spawn them at once - this will prevent overload on the scheduler and allow you to avoid overload (well, complete enslavement of the ChEZ by bandits and mutants, huh).