Cliquet-pusher

- Upgrade to Kinto 6 and Python 3.5

- Fixing some common 500 with the plugin (20)

- Add the plugin version in the capability. (12)
- Handle the `pusher.cluster` option. (17)
- Update to super Kinto 5.0

- Project renamed to _Kinto-fxa_ to match the rename of `cliquet` to
`kinto.core`.
- Update to `kinto.core` for compatibility with Kinto 3.0. This
release is no longer compatible with Kinto < 3.0, please upgrade!

- Add HTML demo with _Kinto_ and _Leaflet_
- Works with _Cliquet_ 2.11

- Initial working proof-of-concept.