SegWit wallet support

This introduces two command line flags (-addresstype and -changetype) which control
the type of addresses/outputs created by the GUI and RPCs. Certain RPCs allow
overriding these (`getnewaddress` and `getrawchangeaddress`). Supported types
are "legacy" (P2PKH and P2SH-multisig), "p2sh-segwit" (P2SH-P2WPKH and P2SH-P2WSH-multisig),
and "bech32" (P2WPKH and P2WSH-multisig).

A few utility functions are added to the wallet to construct different address type
and to add the necessary entries to the wallet file to be compatible with earlier
versions (see `CWallet::LearnRelatedScripts`, `GetDestinationForKey`,
`GetAllDestinationsForKey`, `CWallet::AddAndGetDestinationForScript`).

test/functional/test_runner.py

@@ -86,6 +86,7 @@ BASE_SCRIPTS= [
     'mempool_resurrect_test.py',
     'txn_doublespend.py --mineblock',
     'txn_clone.py',
+    'txn_clone.py --segwit',
     'getchaintips.py',
     'rest.py',
     'mempool_spendcoinbase.py',