add support for re-authentication

as discussed here, https://github.com/facebook/facebook-php-sdk-v4/pull/309

adds a new base method to generate url : makeUrl()
and other  3 methods to get a login URL, re-request URL & re-authentication URL. 
makeUrl() is base(private!) method, and is used by other public Url methods, which only have arguments of $redirectUrl and  $scope array. $params argument gets formed in this calling methods, which do not use(repeat) any of the three default values you mentioned. so, i think it's not necessary for now.