* Properly initialize confirmedHash in CSimplifiedMNListEntry
* Add consensus params for temporary hard-fork on testnet
This hard-fork is required on testnet as we have to fix a few consensus
bugs in DIP3/DIP4. It will also be required to introduce LLMQ commitments
to testnet.
* Add temporary fork-logic for testnet, which sets confirmedHash to null
...before fork activation. Otherwise we'd invalidate all DIP3 blocks on
testnet.
* Bump nTemporaryTestnetForkHeight to 273000