[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`
- [x] image processing worker to resize images
    - [x] worker server
    - [x] computer cluster with gm
    - [x] upload to s3
- [x] put processed images on s3 public bucket
- [ ] domain for s3 public bucket
- [ ] fxa-dev integration
- [ ] docs
    - [x] docs/API.md
    - [ ] docs/DESIGN.md
- [ ] tests
    - [x] tests with img.local driver
    - [ ] tests with img.aws driver

fixes #29 
@seanmonstar If the profile-server doesn't sport front-end browser code, let's change the `browser:true` in [/.jshintrc:4](https://github.com/mozilla/fxa-profile-server/blob/2a4fbf102707d2815f98a24c5da6ae4d50ccf838/.jshintrc#L4) to `false` and this should error everywhere.