Review and potentially rework global exception mapping

[jongeorge1]

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From a comment on exception mapping in a separate PR (marain-dotnet/Marain.ContentManagement#19):

"...I don't really like exception mapping. It configures a behaviour in a global way making it more or less impossible to tell what the actual impact is going to be. I actually have no idea whether this is OK or not because I can't tell what it really does.

There cases where mapping highly specific exceptions to particular responses can be OK, e.g., some very particular error might reliably always correspond to a 404 in a particular application. But what worries me here is that tenancy is a cross cutting concern, and as such, some other 4xx error might well sometimes be appropriate."