Understand array for custom action policy

from now on, it is possible to use array notation for custom actions.

```js
{
    user: {
        findAll: ['foo', 'bar']
    }
}
```
Use policies as a filterChain

For every policy, the `next` callback calls next policy in row and is
called back when finished.

```js
// config/policies.js
{
    user: {
        findAll: ["foo", "bar"]
    }
}
```

```js
// api/policied/foo.js
module.exports = function(req, res, next) {
    console.log('Enter foo');
    next();
    console.log('leave foo');
}
```

```js
// api/policied/bar.js
module.exports = function(req, res, next) {
    console.log('Enter bar');
    next();
    console.log('leave bar');
}
```

Calling `findAll` action would result in the following:

    Enter foo
    Enter bar
    Leave bar
    Leave foo
Merged themouette's fix for chained policies.