Introducing relative times:  feature request #219

This PR is up for discussion, please wait before merging..

Question is: Where do we want relative times? I'd personally go with the frontend only and use  the standard time format inside all logs / admin area.

Next question: Do we need relative times for future events (e.g. poll expire date, calendar events)? I'd favour real dates 

Usage would be: relativeTime() instead of timeformat();