Add hotkey settings panel with a hotkey remap dialog

* Add HotkeyDialogLogic.cs
* Add dialog-hotkey.yaml to all mods
* Add `GetFirstDuplicate` method to HotkeyManager to aid in validation
* Add "Player" and/or "Spectator" type to all hotkeys to allow for
validation based on overlapping types
* Change settings.yaml and SettingsLogic.cs to work with the new dialog

OpenRA.Game/HotkeyManager.cs

@@ -67,6 +67,20 @@ namespace OpenRA
 				settings.Remove(name);
 		}
 
+		public HotkeyDefinition GetFirstDuplicate(string name, Hotkey value, HotkeyDefinition definition)
+		{
+			foreach (var kv in keys)
+			{
+				if (kv.Key == name)
+					continue;
+
+				if (kv.Value == value && definitions[kv.Key].Types.Overlaps(definition.Types))
+					return definitions[kv.Key];
+			}
+
+			return null;
+		}
+
 		public HotkeyReference this[string name]
 		{
 			get