Prettier output of (large) duration values

[Jellix]

Currently we treat a duration the same way as any other unit. While this is fine for duration values less than 1000 seconds or so, it easily becomes unusual, or even unreadable once we start prefixing seconds to express kilo seconds or even Mega seconds (i.e. 1 hour would be expressed as 3.6 ks, one day is 86.4 ks, and one year is about 31.5 Ms). Though technically correct this is not how humans usually express such values.