refs https://github.com/TryGhost/Team/issues/510
- When the host config was introduced it was incorrectly introduced as host_settings instead of hostSettings
- All other Ghost config uses camelCase, so changing this now before it becomes a problem
- Note: Also removed some rogue return awaits that don't make sense. It's not possible to hit that case, but cleaning up anyway
refs: https://github.com/TryGhost/Team/issues/510
- added and wired up the new limit service, which is a lazy-loaded service
- this handles the case that there are host limits set in config, and wraps all the logic needed for detecting exceeded limits & throwing limit errors
- expects limits to be set in config under `host_settings.limits`
- supported limits are managed in the limit service, outside of core
