Bug 1112460 - Keyboard build script changes to optionally preload dict +autoland

So what we're doing is
1. Add a Dict Label in layout file if the Dict it uses is shared by other layouts
2. Each Dict Label must be the same for that Dict ID, across different Layout files (checked here)
Right?

Instead of creating the redundancy and putting the burden of checking for consistency onto the developer modifying the layout files and onto the javascript codes here, I guess we could create an extra mapping JSON file like
``{
 es: {
  label: 'Español',
  layouts: ['es', 'es-Americas']
 },
 'en_us': {
  label: 'English',
  layouts: ['en-Colemak', 'en-Dvorak', 'en-Neo', 'en']
 },
 // others follow
}``