[wip] Avatars

Still a work in progress.

Status:

- [x] `GET /v1/avatar`
- [x] `GET /v1/avatars`
- [x] `POST /v1/avatar`
- [x] `POST /v1/avatar/upload`
- [ ] store images on s3 private bucket
- [x] image processing worker to resize images
- [ ] put processed images on s3 public bucket
- [ ] domain and proxy for s3 public bucket

fixes #29 
Actually, I just found this today:

https://en.gravatar.com/site/implement/images/#secure-images

> #### Secure Requests
> If you're displaying Gravatars on a page that is being served over SSL (e.g. the page URL starts with HTTPS), then you'll want to serve your Gravatars via SSL as well, otherwise you'll get annoying security warnings in most browsers. To do this, simply change the URL for your Gravatars so that is starts with:
> 
> https://secure.gravatar.com/...
> 
> Everything else is the same as above (all the same options work), just make sure that the URL starts out like this.