Update sidekiq to latest version

Add `capistrano-sidekiq` for deploy tasks that were removed in v3 of
`sidekiq`.
Remove `whenever` gem

Use a gem that better integrates with `sidekiq`
Update honeybadger

* Use async option to send error messages in a background worker
* Update to provide sidekiq integration.
* Use `STAGE_NAME` environment variable to customize environment name,
  defaulting to `Rails.env`
* Log exceptions on failure to send
Use `sidetiq` for scheduling background jobs

Add web extension to view status in sidekiq dashboard.
Update sidekiq and related gems

* Updates `sidekiq` to the latest version
* Updates `honeybadger` and its configuration
* Removes `whenever` in favor of `sidetiq` for scheduling background
  jobs