Re-add destroying for unloading, other clean up:

* Cleaned some module terminate code
* Fixed "reload all" issues

modules/client_terminal/terminal.lua

@@ -150,10 +150,8 @@ function terminate()
   g_settings.setList('terminal-history', commandHistory)
   g_keyboard.unbindKeyDown('Ctrl+T')
   g_logger.setOnLog(nil)
-  commandTextEdit = nil
-  terminalBuffer = nil
   terminalWindow:destroy()
-  terminalWindow = nil
+  terminalButton:destroy()
   commandEnv = nil
 end