Main menu screen is slow and can cause lags to another gcode sender connected

[Gerporgl]

See my pull request where I fixed this issue for a detailed description:
#36

I think it is just a great improvement, I have submitted the pull request since some time already, perhaps creating an issue is needed to get a notification and some feedback.

It would be great if someone else could test this and see if they like the new responsiveness of the menu.

Jeeeff