Consider BAI missions planned this turn when determining if a control
point is still garrisioned for preventing breakthrough.
This isn't very accurate yet since the HTN isn't checking for aircraft
fulfillment yet, so it might *plan* a mission to kill the garrison, but
there's no way to know if it will be fulfilled.
This improves the AI behavior by choosing the stances non-randomly:
* Breakthrough will be used if the base is expected to be capturable and
the coalition outnumbers the enemy by 20%.
* Elimination will be used if the coalition has at least as many units
as the enemy.
* Defensive will be used if the coalition has at least half as many
units as the enemy.
* Retreat will be used if the coalition is significantly outnumbers.
This also exposes the option to the player.
Garrison groups should be preferred with the following priority:
1. Groups blocking base capture
2. Groups at bases connected to an active front line
3. Rear guard units
Previously they were being prioritized based on the distance to the
closest friendy control point, which is similar to this but an
aggressively placed carrier could throw it off.
