feat(avatars): profile images

Getting there! Feel free to start looking @shane-tomlinson @pdehaan.

Still needs:
- [ ] profile-server client
- [ ] progress indicator screen
- [ ] unit tests for camera view
- [ ] unit tests for cropper widget
- [x] circular overlay on cropper
- [ ] functional tests
This abuse of `Session` is just to pass data between views. It doesn't actually need to persist beyond that transition.