Hoist _populate_script_map from BIP32Wallet into BaseWallet, rename it
to _populate_maps, and have it populate the new _addr_map in addition to
the existing _script_map. Have the constructor of each concrete wallet
subclass pass to _populate_maps the paths it contributes. Additionally,
do not implement yield_known_paths by iterating over _script_map, but
rather have each wallet subclass contribute its own paths to the
generator returned by yield_known_paths.