New Bangle.js 2 menu system

This is the gist from the start of the thread, modified in the way I described (the non-hacky way).

https://www.espruino.com/ide/?gist=e346a3df9ab3ab26e5f4238c15e8f7f0

The changes required to menu code are:

// First menu
var mainmenu = {
  "" : { "title" : "Main Menu" },
  "< Back" : function() { print("Back") },
  "Submenu" : function() { E.showMenu(submenu); },
};
var submenu = {
  "" : { "title" : "SubMenu" },
  "< Back" : function() { E.showMenu(mainmenu); },
  "One" : undefined, // do nothing
};

becomes:

var submenu = {
  "" : { "title" : "SubMenu" },
  "< Back" : function() { E.showMenu(mainmenu); },
  "One" : undefined, // do nothing
};

// First menu
var mainmenu = {
  "" : { "title" : "Main Menu" },
  "< Back" : function() { print("Back") },
  "Submenu" : { submenu: submenu },
}