Default to paying fees that are less than transfer amount

[Randy808]

I was showing the app to someone new to Bitcoin and they spent more in on-chain fees than the actual transfer amount. The fee rate was almost double the average fee rate of the block it was included within (the next block confirmed).

I’m not sure what the logic is behind having such an aggressive fee rate but it would be good to do some basic checks of the values paid. Maybe this could even include having a setting where a default for transaction priority can be configured.