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`).

src/qt/addresstablemodel.cpp

@@ -384,7 +384,8 @@ QString AddressTableModel::addRow(const QString &type, const QString &label, con
                 return QString();
             }
         }
-        strAddress = EncodeDestination(newKey.GetID());
+        wallet->LearnRelatedScripts(newKey, g_address_type);
+        strAddress = EncodeDestination(GetDestinationForKey(newKey, g_address_type));
     }
     else
     {