Add 'groupings' option to number_to_phone helper

This will allow the method to handle many more countries. For example, mobile phones in Australia use the format "0412 345 678" and landlines use the format "(02) 1234 5678". The 'groupings' option makes generating these formats possible:

number_to_phone('0212345678', :groupings => [2, 4, 4], :area_code => true, :delimiter => " ") # => (02) 1234 5678

number_to_phone('0412345678', :groupings => [4, 3, 3], :delimiter => " ") # => 0412 345 678