(from discussion on IRC. Currently a global `settxfee` has to be changed to override the fee rate, it would make sense to be able to specify it on a per-transaction basis. This would continue #7518)

```
-*- jonasschnelli thinks we should probably add a optional feerate parameter to fundrawtransaction
<wumpus> jonasschnelli: there isn't one yet?
-*- jonasschnelli looking..
<wumpus> I'm surprised, would be so much better than changing a global
<jonasschnelli> no.. i don't think so. Maybe there is a PR.
<sipa> there is a pr
<jonasschnelli> Hard to keep track of everything. :)
<wumpus> no, the PR does it wrong
```

Regarding implementation:

```
<jonasschnelli> The ugly thing is, that CreateTransaction uses the static DEFAULT_TARGET
<wumpus> passing in an optional feerate would be the obvious thing to do
<jonasschnelli> So, this would require some refactoring.
<sipa> just add a confirmation target to coincontrol
<jonasschnelli> Yes. This sounds good.
<wumpus> right, just slap it into coincontrol
<sipa> wasn't there a PR that added a bunch of options to fundrawtransaction?
<sipa> including that
<jonasschnelli> Not the feerate.
<jonasschnelli> But the rest is merged.
```

{
    map<CTxDestination, CAmount> balances;
    {
        LOCK(cs_wallet);
        BOOST_FOREACH(PAIRTYPE(uint256, CWalletTx) walletEntry, mapWallet)
        {
            CWalletTx *pcoin = &walletEntry.second;
            if (!CheckFinalTx(*pcoin) || !pcoin->IsTrusted())
                continue;
            if (pcoin->IsCoinBase() && pcoin->GetBlocksToMaturity() > 0)
                continue;
            int nDepth = pcoin->GetDepthInMainChain();
            if (nDepth < (pcoin->IsFromMe(ISMINE_ALL) ? 0 : 1))
                continue;
            for (unsigned int i = 0; i < pcoin->vout.size(); i++)
            {
                CTxDestination addr;
                if (!IsMine(pcoin->vout[i]))
                    continue;
                if(!ExtractDestination(pcoin->vout[i].scriptPubKey, addr))
                    continue;
                CAmount n = IsSpent(walletEntry.first, i) ? 0 : pcoin->vout[i].nValue;
                if (!balances.count(addr))
                    balances[addr] = 0;
                balances[addr] += n;
            }