Support multiple hooks per action

[1602]

It should be possible to add multiple hooks per action. Also let's get rid of mixin-style hooks declaration. Hook should return promise.

User.afterCreate = function(data, done) {
    Basket.create({userId: this.id}, (err, basket) => {
        done(err);
    });
};

should become

User.hooks.after('create', user => Basket.create({userId: user.id}));

Old mixin-style should be deprecated from next stable version.