Purchases: improve feedback when updating payment details

[fabianapsimoes]

It currently takes a while to save new credit card details from Edit Card Details. After clicking the Update Card button, nothing happens and there is no notice to let users know their new details are being saved. The operation is being processed though, there's just no feedback. After a while, a green notice shows letting the user know the new credit card was saved successfully.

We should improve the feedback after clicking Update Card, so it's clearer to users we're working on their request.

cc @mikeshelton1503

[mikeshelton1503]

I will need to think through this some more but we need a better loading/processing state component for actions like this. The same type of issue exists in checkout. I designed a new processing losing state in 5087-gh-calypso-pre-oss that I think will work here too.

https://cloudup.com/cKrzdRZS0j2

[fabianapsimoes]

To begin with, we should make sure to at least disable the button in Edit Payment Details. We can look into a more general solution to improve processing states later on.

[fabianapsimoes]

Removing from Amber: Backlog as this would be better handled by Team Gold. cc @melanieharari