Add Instagram Adapter

It uses the following entry point:

`https://api.instagram.com/v1/users/{USER_ID}/media/recent?client_id={CLIENT_ID}`

This is so that you do not need an `access_token`.

**Limitations**
 - Does not support multiple pages. Looks like you'll get ~32 results per page.
*note: You can use `'count' => -1` to get all results at once, but it's costly.*
 - Does not support any data besides images and videos. No likes, comments, etc.