Update to Neo3-preview4

[danwbyrne]

Quick checklist summarizing the commits / changes that have been made between preview3 and preview4 we'll need to implement.

While it may look daunting many of these commits will be taken care of in 1 commit since many of them are overlapping changes, for example adding the new native contracts will take care of any of these "optimize" commits I organized.

• remove testMode from applicationEngine Remove testmode from ApplicationEngine neo-project/neo#1819
• update isMultisigContract method Fix IndexOutOfRangeExceptions from IsMultiSigContract neo-project/neo#1890
• new CheckReturnType enum look into its use Call _deploy during deploy and update neo-project/neo#1933
• Fix witness script limits Fix Witness limits neo-project/neo#1958
• investigate this 'fix native serialize' change Fix native serialize neo-project/neo#1988
• update MaxValidUntilBlock Move MaxTraceableBlocks to protocol neo-project/neo#2042
• check this https://github.com/neo-project/neo/pull/2106/files
• add 'data' property to Transfer https://github.com/neo-project/neo/pull/2112/files
• call flag changes Fix CallFlags neo-project/neo#2121
• scriptbuilder Add CreateArray and CreateMap to Helper neo-project/neo#2145
• more transaction cost changes https://github.com/neo-project/neo/pull/2149/files
• 'nativeActivations' to protocol settings Refactor native activation block Index neo-project/neo#2141

Blockchain changes:

• investigate this change for calculating verificationCost Allow to search verification script in witnesses neo-project/neo#1931 done but verify
• onPersist / postPersist + trigger changes Different Trigger for OnPersist and PostPersist neo-project/neo#2022
• asynchronous oracle blockchain changes Asynchronous Oracle neo-project/neo#1738
• check these changes in blockchain for oracle Fix incentive for committee neo-project/neo#1884

Node changes:

• Add ping expiration (seems low priority) [neo3] Add Ping expiration neo-project/neo#1829
• 'Optimize Ping Message' Optimize Ping message neo-project/neo#1903
• update transaction verification process (needs investigation) Relocate transaction verification neo-project/neo#1507
• investigate this block receive height limit change Add block receive height limit neo-project/neo#1870
• will these compression changes affect us ? Optional p2p compression neo-project/neo#1906
• Oracle payload stuff Add oracle InsufficientFunds code neo-project/neo#2037
• https://github.com/neo-project/neo/pull/2097/files
• transactionVerificationContext now has some oracle logic Fix Oracle PostPersist neo-project/neo#2074
• https://github.com/neo-project/neo/pull/2054/files

Native Contract Changes:
(a lot of these overlap and will be checked off in one go)

• Optimize BlockAccount in native Policy contract Optimize BlockAccount neo-project/neo#1843
• update native contracts for incentive changes (fairly substantial) Add incentive for neo holders neo-project/neo#1845 Add incentive for committee neo-project/neo#1847
• another neo token update Initialize next validators neo-project/neo#1917
• add committee cache changes Cache committee in storage neo-project/neo#1920
• investigate this "fix candidate" change Fix candidate neo-project/neo#1935
• Policy contract changes Policy inputs checks neo-project/neo#1938
• 'Designate' contract Add Designate contract neo-project/neo#1950
• 'fix verifywitnesses()' of native contracts (we might not need this?) Fix VerifyWitnesses() of native contracts neo-project/neo#1998
• other voter incentives Add incentive for voter neo-project/neo#1848
• oracle / designate contract changes Add role designation history neo-project/neo#2007
• more reward changes Distribute more GAS reward for committee neo-project/neo#2049
• oracle contract Add oracle Request/Response event neo-project/neo#2036
• NEP17 Implement NEP-17 neo-project/neo#2024
• management contract Create ManagementContract neo-project/neo#2119
• adjustable opcode pricing SmartContract/Native: implement adjustable opcode pricing neo-project/neo#2045
• asset symbols https://github.com/neo-project/neo/pull/2136/files
• minimum deployment fee Add MinimumDeploymentFee neo-project/neo#2140

Consensus Changes:

• Optimize LastSeenMessage in ConsensusContext Fix #1834 neo-project/neo#1838
• set lastBlockIndex during checkCommits consensus: set last_block_index during CheckCommits neo-project/neo#1960
• optimize nextConsensus Optimize NextConsensus neo-project/neo#2015