Add segwit and charge txfee to receiver

[debreczeni]

• Updating BitGoJS from 2.x to 4.x will make bitgo use segwit addresses for transaction fee discount
• Deduct fee from outgoing bitcoin transaction amount

Possible improvements:

• display actual fee and amount - fee to customer on screen
• persist fee and actual amount separately in db
• add admin config for tx fee calculation parameters
• add admin config for transaction fee policy (we pay, they pay, shared, etc...)