[REQUEST] ETA as a variable

[SillyHats]

It would be great if ETA could be a status variable in messages. I have gotten used to seeing it in the side bar of the web interface and it makes it a bit nicer to not have to do the math of current time + remaining time each time I look at the status message.

[rlogiacco]

In the next release ETA will be available as {time_finish}