Cliquet-fxa

**Bug fixes**
- Make sure that caching of token verification nevers prevents from authenticating
requests (see Mozilla/PyFxA48)

**Internal changes**
- Migrate schemas to Cornice 2 38

**New features**
- Improve FxA error messages (fixes 1)

**Bug fixes**
- Optimize authentication policy to avoid validating the token several times
per request (fixes 33)

**Internal changes**
- Use Service from kinto.core (fixes 28)
- Make sure it does not catch Cornice 2 dependency (36)

- Add the plugin version in the capability.

**Breaking changes**
- 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!
- With _Kinto_ > 2.12*, the setting `multiauth.policy.fxa.use` must now be explicitly set to `kinto_fxa.authentication.FxAOAuthAuthenticationPolicy`

**Bug fixes**
- Fix checking of `Authorization` header when python is ran `-O` (ref mozilla-services/cliquet592)

- Updated to _Cliquet_ 2.9.0

**Breaking changes**
- _cliquet-fxa_ cannot be included using `pyramid.includes` setting.
Use `cliquet.includes` instead.