This commit changes how timelocked addresses are created from the seed and bip32 tree.
A good thing to do would be to have each locktime (e.g. 1st jan 2020,
1st feb 2020, 1st march 2020, etc) actually use a different pubkey from
the HD tree (i.e. ("m/84'/1'/0'/2/0" + 1st jan 2020) ("m/84'/1'/0'/2/1" + 1st feb 2020), etc).
This now means that the sync code doesnt need to know what keys have been associated with
a fidelity bond to scan for the next one. Previously when a user funded a single timelocked
address, the wallet will generate _another_ pubkey and import _another_ ~960 addresses, so
funding one address would actually mean watching and generating ~1920 addresses not ~960.
This should help with the problem found by some people that fidelity bond wallets are slower
to sync. Other optimizations are possible but the structure of fidelity bond wallets will
probably be fixed for decades, so this change is worth doing now.
chris-belcher
c70b12f614