Progressively load gas estimations on confirm screen

[bdresser]

Right now, we block rendering the confirmation screen on gas estimation. We should render the screen, then fill in gas estimation inline to improve the loading time of confirmation screens.

[PhABC]

Please also allow for manual imput even if gas estimation and gas price aren't loaded. Right now, I personally can't manually set the gas price as my confirmation screen is stuck, as follow.

I am unable to manually change the gas price and gas limit value until the charts are loaded, which takes a very long.