Feature request: Add ICP to fiat currency convertion to the "Send ICP" page.

[evanstucker-hates-2fa]

Go to https://nns.ic0.app/, click Tokens, then click Internet Computer. Note that the ICP to USD convertion is provided here.

Click on Main, then click Send. If we want to send someone $26 USD worth of ICP token, we have to open a calculator app and do the math manually. It would be nice if we could instead click a "USD" button to change the currency input field to use USD (and display the ICP amount below the input box.)

While we're at it, we should be able configure the type of fiat currency to any currency, not just USD.