Handle unmanaged traits via ManagementPolicy

[elliotcmorris]

Ensure unmanaged locatableContent trait queries are always passed through to the default resolver, and that we're not calling resolve on them. Devise an efficient way to test this.

[feltech]

We should probably error, rather than pass through to the default resolve (i.e. file system), since we would know that we're dealing with an entity reference. We are already throwing a runtime_error.