Refactor translation files

- Add prefixes to all message keys to provide context
- Use messages with attributes for some UI elements (dropdowns, dialogs, checkboxes, menus)
- Rename some class fields for consistency with translation keys

OpenRA.Mods.Common/Commands/ChatCommands.cs

@@ -23,7 +23,7 @@ namespace OpenRA.Mods.Common.Commands
 	public class ChatCommands : INotifyChat
 	{
 		[TranslationReference("name")]
-		const string InvalidCommand = "invalid-command";
+		const string InvalidCommand = "notification-invalid-command";
 
 		public Dictionary<string, IChatCommand> Commands { get; }