Catch Finish singnal from Printer

[j0sh21]

The basics of this Method are already there, but maybe not configured correctrly.
As a kind of HotFix the code waits 50 secounds hardcoded.
It Would be very nice to get detaild print job status, like (starting, heating up, printing yellow, priniting red...) the cups api should offer this functionallity. Dox Box already uses CUPS for sending print jobs.