add chat panel, send text messages, guard forbidden functions with an ifdef

modules/chat/chat.lua

@@ -0,0 +1,19 @@
+Chat = {}
+
+-- private variables
+local chatPanel
+
+-- public functions
+function Chat.create()
+  chatPanel = loadUI("/chat/chat.otui", Game.gameBottomPanel)
+end
+
+function Chat.destroy()
+  chatPanel:destroy()
+  chatPanel = nil
+end
+
+-- hooked events
+
+connect(Game, { onLogin = Chat.create,
+                onLogout = Chat.destroy })