Gmail "View Topic" button in forum notifications, exp. 2

There is a nice integration between Gmail and Github for notifications in GitHub Issues and Pull Requests: Gmail shows a "View Issue" / "View Pull Request" button directly in the message list. At first I thought this is something Gmail does for GitHub specifically, based on message headers like List-Archive and List-Unsubscribe. But looking at the source code of a GitHub notification I found that there's a snippet of JSON attached at the end. It's a schema.org schema which describes an action that an user-agent may expose to the user - and it's something that anybody sending an e-mail may include. So I'm trying it out now for Nittro Forums notifications. We'll see how it goes :-)

@jahudka let's see how it works!

@jahudka how about now?

@jahudka and now?

@danik still nothing?

@jahudka nope :-(

@jahudka ... this is getting old fast..

@jahudka well.. we've successfully broken everything, then fixed it again and then found out that Google won't display our shiny buttons unless we send "on the order of hundreds [of messages to Gmail] weekly".. so there's that. Damn you Google! But our code is now correct, at least.