Refactor importing BTC addresses into son-wallet

Currently, we use importaddress RPC call to import primary wallet and deposit addresses into BTC wallet used by SONs.

Due to chain rescan that executes on address import, wallet is unavailable for some time, and only very few addresses are actually imported. This prevents SONs to track and query transactions.

Importing primary wallet and deposit addresses should be refactored to use importmulti RPC, to import all addresses in one go, and limit rescaning time from HARDFORK_SON_TIME only.