Support sending an authenticated Reply-To address as part of a transaction memo.

[nuttycom]

Is your feature request related to a problem? Please describe.

For many use cases, it's important to be able to reply to someone who sent you a message, or to be able to return funds to the sender of a transaction.

Describe the solution you'd like

The user should be able to click on a checkbox next to the memo field that says "Include a reply-to address". This might take up some part of the memo space, so it could affect memo length, but there are also designs whereby the reply-to address would be sent separately.

Someone receiving such a transaction should see the reply-to address in their wallet UI, should be able to click on that address to send a reply, and should see a little lock icon if the transaction contains a proof that funds that were spent in the sending of this transaction were controlled by the same keys as control spending authority for any funds that may be sent to the reply-to address.

If the authentication check described above fails, the reply-to address should be hidden or marked as potentially unsafe.

We should also potentially scan received memos for strings that parse according to the old text reply-to convention, and such reply-to addresses should also be hidden or marked as unsafe.