Amount in Receive doesn't respect display settings

[slush0]

Hello,

when user choose to see balances and amounts in fiat currency, he still sees "sats" as default option when editing payment request. It is still possible to choose fiat currency from the dropdown but it would be a nice final touch to respect the display settings in this dialog, too.

Another nice improvement would be to have UI focus to amount input box in the dialog by default as it is likely the only value user wants to edit here.

Implementing these two tiny changes would improve the user experience a lot for a coffee bar where I'm implementing Phoenix. By the way, I love Phoenix!