* replace bitvec with more efficient bitpack algorithm
* optimise proof_unpack_len
* move proof pack length calculation
* small refactor
* first pass attempt at not deserializing proof nonces in difficulty iter
* another 10 seconds gained by not deserialising the proof from the difficulty iterator
* add new deser parameters to tests where needed
* add skip_proof variants to store
* remove hash from difficulty iterator struct, rename HeaderInfo to HeaderDifficultyInfo
* replace bitvec with more efficient bitpack algorithm
* optimise proof_unpack_len
* move proof pack length calculation
* small refactor
* first pass attempt at not deserializing proof nonces in difficulty iter
* another 10 seconds gained by not deserialising the proof from the difficulty iterator
* add new deser parameters to tests where needed
* add skip_proof variants to store
* remove hash from difficulty iterator struct, rename HeaderInfo to HeaderDifficultyInfo
* HardFork4 initial commit
* HF4 obsoletes secondary_scale, which becomes an nonce extension 8->12 bytes
* fix TESTNET_FOURTH_HARD_FORK height
* improve predicted height for testnet fork on dec 8
* move local variable as suggested by antiochp
* Introduce GLOBAL_CHAIN_TYPE and make CHAIN_TYPE thread_local.
This makes testing more explicit and significantly more robust.
* set_local_chain_type() in tests
* cleanup - weird
* get pool tests working with explicit local chain_type config
* core tests working with explicit local chain_type
* p2p tests working with explicit local chain_type
* store tests working
* cleanup, feedback
