Agent status page

This adds a status page for both agents, if the event of one needing to know what exists inside the agent of an instance at any given time.

Since I see this as properties of the instance, I have added them to the management pages. This could be moved to `FaciaController` in the future if someone would like to make use of the contents; for either JS or healthchecks.

For the `CollectionAgent`, it just outputs each collection as a key in a map, and a corresponding list of `Item IDs` that exist for this ID.

For the `ConfigAgent`, we just dump out the JSON.