[ADDED] getrealbalance wrapper for payouts

During payouts, we must ensure our wallets main accounts has the funds
to payout users. Hence we implement a wrapper method:

* If account count == 1 we only have main account, return getbalance
* Else return our main accounts balance - calculated unconfirmed

This should keep getbalance untouched when used on other places but
gives our payout processing a proper main account balance.

It's mostly a wrapper for those wallets running multiple accounts in one
wallet. They are warned on the front-end already but this ensure payouts
process properly.

Fixes #1755 once merged.