Implementation of the alt and copyright fields in image views

They are in the JSON, so I'm thinking, they could be useful.

```json
{
  "main": {
    "url": "https://prismic-io.s3.amazonaws.com/lesbonneschoses/79a7a068ceb47892ac8de2480e878962d8b93cc6.png",
    "alt": "",
    "copyright": "",
    "dimensions": {
      "width": 500,
      "height": 500
    }
  },
  "views": {
    "icon": {
      "url": "https://prismic-io.s3.amazonaws.com/lesbonneschoses/b12819d149a0e6c6cd6717dba4b2c6a1bdafa9d4.png",
      "alt": "",
      "copyright": "",
      "dimensions": {
        "width": 250,
        "height": 250
      }
    }
  }
}
```

Of course, tested and all.