Rename doublejump to airjump (#348)

Author: Panzerhandschuh

db/factories/momentum.txt

@@ -230,8 +230,8 @@ momentary_door
 momentary_rot_button
 momentum_df_weaponspawner
 momentum_generic_bomb
+momentum_powerup_airjump
 momentum_powerup_damageboost
-momentum_powerup_doublejump
 momentum_powerup_flight
 momentum_powerup_haste
 mom_replay_playback

fgd/point/momentum/momentum_powerup_airjump.fgd

@@ -0,0 +1,7 @@
+@PointClass base(MomentumPickup)
+	appliesto(MOMENTUM)
+	size(-43 -43 -36, 43 43 66)
+= momentum_powerup_airjump : "Air Jump Powerup"
+	[
+	SingleUse(boolean) : "Single Use" : 1 : "When enabled, the air jump does not refresh on landing and the powerup is removed as soon as the player air jumps."
+	]

fgd/point/momentum/momentum_powerup_doublejump.fgd

@@ -858,7 +858,7 @@
 		* `momentum_powerup_flight`
 		* `momentum_powerup_haste`
 		* `momentum_powerup_damageboost`
-		* `momentum_powerup_doublejump`
+		* `momentum_powerup_airjump`
 
 	- World Details
 		- Func Detail (`func_detail`)