Add easy generation of one-off email addresses

[ScottPeterJohnson]

(This issue was imported from Gitea) Scott on February 28, 2019: A more robust version of #9.

• Generate plausible email addresses that route back to an actual user

• May be most convenient as a browser extension?

• Allow replies appearing as if from these addresses

This basically improves the flow of handing out email addresses, so you can give a fake email address to a possibly spammy site and block the fake address entirely later.