Entering optional fee addresses for assets.

[Germardies]

Optional fee addresses have been added to all asset instructions in the Raptoreum CLI.
An asset change address has been added specifically for sendasset.

[JSanchezFDZ]

Reviewed the optional asset fee-address feature.

1. Scope / duplicate. This PR's head (eb4a1ea) is the same commit as #438, so
   it also contains the entire auto-bootstrap downloader plus lockedpool.cpp,
   bip32.h, and .gitignore changes. The actual fee-address change is only part
   of rpc/rpcassets.cpp. Please rebase so this PR contains just the feeAddress
   feature and close/separate #438 — otherwise the (security-sensitive) bootstrap
   code blocks an otherwise small asset feature. The bip32.h <cstdint> and
   lockedpool.cpp <stdexcept> additions are legitimate build fixes but unrelated;
   fine to keep, but please call them out or split them.

2. Feature itself. The approach across createasset/sendasset/mintasset
   (DecodeDestination + IsValidDestination, coinControl.destChange = feeDest,
   manual selection of feeDest UTXOs, fAllowOtherInputs = false) reads
   reasonably. Two things to confirm:

   • With fAllowOtherInputs = false and only feeDest UTXOs selected, please
     verify the asset funding inputs/outputs still resolve for all three RPCs — a
     feeAddress that holds RTM but where the asset/owner outputs would need other
     inputs could fail in a way users won't expect.
   • The "no spendable UTXOs on feeAddress" path throws
     RPC_WALLET_INSUFFICIENT_FUNDS, which is good; a functional test covering
     that path and "change returns to feeAddress" would make this much easier to
     merge with confidence.