added Flickr drop-in

The Flickr drop-in uses oauthlib directly for OAuth1 operations. This may be interesting as a future model for OAuth1 drop-ins without an additional library.
It doesn't, I was confused about that! Flickr's authorization screen has a cancel button whose source is

```html
<input value="NO THANKS" onclick="window.location = '/'; return false;" class="CancelButt" type="button">
```
So if you click Cancel it just redirects you to flickr.com, not back to the application with an indication that the user declined. Weird right?