Add initial change to allow 2 form pluralities.

Tested with English (US).

Once specified with plurality, the non-plural form cannot be used
i.e.
'en': {
    '&plural-forms': 'nplurals=2; plural=(n!=1)',
    '&plurals': [
        {
            '%phrase1': 'This is the only allowable form'
        }
    ],
    '%phrase1': 'This is COMPLETELY ignored'
}