Feature/Fix: Date-Time from ${X-Received}

[jpfieber]

I'm unable to get ${X-Received} to render. I was trying to use it to get the date and time from so I could use that to rename the file (I want to start the filename with 'yyyymmdd_hhMMss'). If you're diving into the code anyway, would it be possible to make available a ${DateTime} variable that provides the date/time in a common format (something predictable like 'YYYY-MM-DDTHH:mm:ssZ' or an option for multiple common formats)?

[anicholson]

Hey @jpfieber, I don't have heaps of time to dedicate, but I will take a look. PRs welcome if you're at all comfortable in Typescript :)