Add Duration as a standard formatter

[Veejer]

I had originally added this to issue #75 but I don't think anyone is really implementing any of those suggestions. So I am creating a separate ticket for this.

I would like a formatter created and named 'duration'. It should takes an integer of Seconds and convert that to a duration, formatted like HH:MM:SS. Here are some examples:
18,563 seconds = 5:09:23
563 seconds = 9:23
23 seconds = 23
0 seconds = blank

As a separate but related formatter, I would like a 'duration-h' created. This should return the same value as 'duration' but with one difference. If the hours portion is greater than 24, then the number of days would be shown. Here is an example:
91,815 = 1d 1:30:15
90,015 = 1d 0:00:15