Shortcut Alt+M to open Menu tree

As contributed by here:
https://groups.google.com/d/msg/idempiere/lw6MNWB4faA/kNVAvr_9AQAJ

Hi

I have made a patch in order to solve an issue I have had for a long time, that is the possibility for opening the menu by using the shortcut ALT+M and then being able to open the window by pressing the enter key.

ALT+M open the menu.

Enter open the selected window.

ESC close the menu.

Attached a patch for this improvement

/FLemming