[wip] Add site connections endpoints

This adds support for the following REST API endpoints:

- GET `/v1.1/me/publicize-connections`
- GET `/v1.1/sites/$site/publicize-connections`
- GET `/v1.1/sites/$site/publicize-connections/$connection_id`
- POST `/v1.1/sites/$site/publicize-connections/new`
- POST `/v1.1/sites/$site/publicize-connections/$connection_id/delete`