Show synthesized splitfile cryptokey for top block

In some cases KeyExplorer fails to show splitfile cryptokey in top block (always with single-block redirects, but sometimes for splitfiles too).
Show synthesized splitkey in this case.
FIXME Probably this is incorrect in some corner cases.
Merge remote branch 'operhiem1/Eleriseth-showcryptokey'
Fix KeyUtils for changes to HashResult in fred.
Build 5019