Investigate issue of "Threat Level" increasing before enemies have actually spawned

[AidanTweedy]

It appears that the "Threat Level" of the current moon, which is determined with RoundManager.Instance.currentEnemyPower, is updated when an enemy is chosen to spawn, not when it actually spawns. This results in the threat level increasing before the enemy is spawned from a vent.

My proposed solution to this is to calculate the current threat level by checking the list of currently spawned entities, rather than relying on the RoundManager's number.

In addition, the threat level system needs to be tweaked slightly to properly account for inside vs outside power levels.