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/Widgets/Logic/Lobby/KickSpectatorsLogic.cs

@@ -17,7 +17,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 	class KickSpectatorsLogic : ChromeLogic
 	{
 		[TranslationReference("count")]
-		const string KickSpectators = "kick-spectators";
+		const string KickSpectators = "dialog-kick-spectators.prompt";
 
 		[ObjectCreator.UseCtor]
 		public KickSpectatorsLogic(ModData modData, Widget widget, int clientCount, Action okPressed, Action cancelPressed)