* Split keyIDMasternode into keyIDOwner/keyIDOperator/keyIDVoting
keyIDOwner is the key used for things which should stay in control of the
collateral owner, like proposal voting.
keyIDOperator is the key used for operational things, like signing network
messages, signing trigger/watchdog objects and trigger votes.
keyIDVoting is the key used for proposal voting
Legacy masternodes will always have the same key for all 3 to keep
compatibility.
Using different keys is only allowed after spork15 activation.
* Forbid reusing collateral keys for operator/owner keys and vice versa
* Bump SERIALIZATION_VERSION_STRING in CMasternodeMan
