Flickr integration

Environment variables for configuration
```
FLICKRAPIKEY = Flickr API key
FLICKRHASHTAG = Flickr hashtag used for search
FLICKRUSERID = Flickr userid used for search
[FLICKRPERPAGE] = Flickr feed size, default: 20
```

* `GET /api/v1/flickr/tag`
* `GET /api/v1/flickr/user`