Added mapAnchors consensus rules, finished zcrawpour/zcrawreceive.

Some specifics on consensus changes:
* Transactions must be anchored to a real anchor in the chain.
* Anchors are pushed and popped during ConnectBlock/DisconnectBlock as appropriate.
* DisconnectTip triggers evictions, under some circumstances, of transactions in the
  mempool which are anchored to roots that are no longer valid.
* Commitments append to the tree at the current best root during ConnectBlock.

src/wallet/wallet.h

@@ -616,6 +616,7 @@ public:
     void SyncTransaction(const CTransaction& tx, const CBlock* pblock);
     bool AddToWalletIfInvolvingMe(const CTransaction& tx, const CBlock* pblock, bool fUpdate);
     void EraseFromWallet(const uint256 &hash);
+    bool WitnessBucketCommitment(uint256 &commitment, libsnark::merkle_authentication_path& path, size_t &path_index, uint256 &final_anchor);
     int ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate = false);
     void ReacceptWalletTransactions();
     void ResendWalletTransactions(int64_t nBestBlockTime);