SH-4490 More 'humane' error code presentation from llcorehttp callers

Added toTerseString() conversion on HttpStatus to generate a string
that's more descriptive than the hex value of the HttpStatus value
but still forms a short, searchable token (e.g. "Http_503" or
"Core_7").  Using this throughout the viewer now, no live cases
of toHex(), I believe.