add `toPrettyDuration` to prettify a duration
add `toPrettyDuration` to prettify a duration

`toPrettyDuration` takes seconds and converts the value into a pretty
format with days, minutes, hours and seconds. It excludes all fields
that are unnecessary.

	modified:   web/js/coge/utils.js

LyonsLab/coge,asherkhb/coge,asherkhb/coge,asherkhb/coge,LyonsLab/coge,asherkhb/coge,LyonsLab/coge,asherkhb/coge,LyonsLab/coge,LyonsLab/coge,asherkhb/coge,LyonsLab/coge,LyonsLab/coge,asherkhb/coge,asherkhb/coge,asherkhb/coge,LyonsLab/coge,LyonsLab/coge