gcode to contain remaining time and/or percent complete

[s3030150]

Would be awesome to have these small data in the gcode. It should not be hard to put a new lines before each layer which contains "estimated time left", "percent complete" and/or "current_layer/total_layers". Three commented lines so we can choose what to process in the post processing script in S3D and show values we want to display.

Should not be so much difficult, since S3D already has all of these data when the gcode is generated, huh?