Co-authored-by: Dagur Valberg Johannsson <dagurval@pvv.ntnu.no>

# Conflicts:
#	qa/rpc-tests/wallet_sapling.py

# Conflicts:
#	src/wallet/rpcdump.cpp

# Conflicts:
#	src/wallet/rpcwallet.cpp

# Conflicts:
#	src/Makefile.am
#	src/zcash/Address.cpp

This fixes the dependency graph between the general address-handling
logic, ZIP 32, and the core Sapling address classes.

# Conflicts:
#	src/Makefile.am
#	src/gtest/test_keys.cpp
#	src/key_io.h
#	src/keystore.h
#	src/wallet/wallet.cpp
#	src/zcash/Address.hpp

All of these maps are created from scratch on wallet load, so we can
alter their contents without compatibility concerns. With this change,
we can use the existing maps to implement viewing key support. The
downside is that the wallet will take more space in memory, but that can
easily be improved in future by storing ExtFVK fingerprints in some of
the maps (which would improve memory usage even compared to the original
layout).

# Conflicts:
#	src/keystore.cpp
#	src/keystore.h
#	src/wallet/crypter.cpp
#	src/wallet/crypter.h

Now that we store SaplingExtendedFullViewingKey internally, we have
access to the default address everywhere we require it.

# Conflicts:
#	src/wallet/crypter.cpp

# Conflicts:
#	src/key_io.cpp

# Conflicts:
#	src/key_io.cpp

# Conflicts:
#	src/wallet/rpcdump.cpp

# Conflicts:
#	qa/rpc-tests/wallet_sapling.py
#	src/wallet/rpcdump.cpp
#	src/wallet/wallet.h

# Conflicts:
#	qa/rpc-tests/wallet_persistence.py

Closes zcash#2937.

# Conflicts:
#	src/wallet/rpcdump.cpp

# Conflicts:
#	src/wallet/rpcdump.cpp