Support the new v2 API permissions format.

Facebook v2 API permissions are returned in a different format to v1. See [v1](https://developers.facebook.com/docs/graph-api/reference/v1.0/user/permissions) vs. [v2](https://developers.facebook.com/docs/graph-api/reference/v2.0/user/permissions) documentation.

Instead of:

```
{ "publish_actions": 1, ... }
```

... we now get:

```
[{ "permission": "publish_actions", "status": "granted" }, ...]
```

I was hesitant to dive into adding v2 support in [fb_graph-mock](https://github.com/nov/fb_graph-mock), so the tests are a bit of a hack.
Yes we are - we run a whitelabel service that has a lot of existing clients with v1 apps, and new ones starting up with v2 apps, running on the same servers. We're working through the approval process to upgrade v1 apps but there's a lot of them, and we need to retain their ability to use :publish_actions while we're migrating.