Generate weather conditions at turn start.

Weather and exact time of day information is helpful during mission
planning, so generate it at the start of the turn rather than at
takeoff time.

Another advantage aside from planning is that we can now use the wind
information to set carrier headings and takeoff runways appropriately.

game/event/event.py

@@ -12,7 +12,6 @@ from game import db, persistency
 from game.debriefing import Debriefing
 from game.infos.information import Information
 from game.operation.operation import Operation
-from gen.environmentgen import EnvironmentSettings
 from gen.ground_forces.combat_stance import CombatStance
 from theater import ControlPoint
 from theater.start_generator import generate_airbase_defense_group
@@ -42,7 +41,6 @@ class Event:
 
     operation = None  # type: Operation
     difficulty = 1  # type: int
-    environment_settings = None  # type: EnvironmentSettings
     BONUS_BASE = 5
 
     def __init__(self, game, from_cp: ControlPoint, target_cp: ControlPoint, location: Point, attacker_name: str, defender_name: str):