Improve pause-return-missed detection

[florianbeisel]

We can easily detect whether the user is likely to have missed booking in when they return from work.

• Detect if user has started a break
• Note when the system goes idle
• If the system returns from idle and the user hasn't checked in after ten minutes notify him that he has likely forgotten

This will of course miss the case where the user stays at his machine and surfs the web in which case the system wont be idle.
This can be caught through a fallback that we already have - does the user exceed is configured break time allotment.