Showing that 1.76 minutes are left sucks a lot, it's much prettier saying "1 minute and 43 seconds"

Introduce KLocale::prettyFormatDuration that gives you a pretty textual form.

The prettyness comes from only showing the user the meaningful info, that is, for example, if one day is left, only shown hours, not minutes nor seconds because you don't actually care for that.

Did this together with ereslibre, got some input from Chusslove