Add a lint test for audio notifications.

Only traits are linted - the UI still hardcodes
too many audio references for this to be worthwhile.

OpenRA.Mods.Common/Traits/SupportPowers/ParatroopersPower.cs

@@ -26,6 +26,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly int SquadSize = 1;
 		public readonly WVec SquadOffset = new WVec(-1536, 1536, 0);
 
+		[NotificationReference("Speech")]
 		[Desc("Notification to play when entering the drop zone.")]
 		public readonly string ReinforcementsArrivedSpeechNotification = null;
 

OpenRA.Mods.Common/Traits/SupportPowers/ProduceActorPower.cs

@@ -26,10 +26,12 @@ namespace OpenRA.Mods.Common.Traits
 		[Desc("Production queue type to use")]
 		public readonly string Type = null;
 
+		[NotificationReference("Speech")]
 		[Desc("Notification played when production is activated.",
 			"The filename of the audio is defined per faction in notifications.yaml.")]
 		public readonly string ReadyAudio = null;
 
+		[NotificationReference("Speech")]
 		[Desc("Notification played when the exit is jammed.",
 			"The filename of the audio is defined per faction in notifications.yaml.")]
 		public readonly string BlockedAudio = null;

OpenRA.Mods.Common/Traits/SupportPowers/SupportPower.cs

@@ -32,16 +32,33 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly string[] Prerequisites = { };
 
 		public readonly string BeginChargeSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string BeginChargeSpeechNotification = null;
+
 		public readonly string EndChargeSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string EndChargeSpeechNotification = null;
+
 		public readonly string SelectTargetSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string SelectTargetSpeechNotification = null;
+
 		public readonly string InsufficientPowerSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string InsufficientPowerSpeechNotification = null;
+
 		public readonly string LaunchSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string LaunchSpeechNotification = null;
+
 		public readonly string IncomingSound = null;
+
+		[NotificationReference("Speech")]
 		public readonly string IncomingSpeechNotification = null;
 
 		[Desc("Defines to which players the timer is shown.")]