Make the HST model fine-grained reloading more resilient and auto-fixed after it is corrupted (cloned for testing on 7.8)

If for some reason (strange invalidation events, fine grained reloading bugs, or whatever that can break hst model loading) the hst model does not succeed finegrained-reloading, use a fallback mode to do a fullblown reload.

Note, that in case of a full blown reload after a failed fine grained reload, we log must log warnings : That way, we can trace back when and how often a fullblown reload is done