add relative date to comment update and create time

[bahamas10]

This change uses the module human-time to turn Date objects into strings that give a relative time, like 5 minutes ago, 2 days ago, 4 months ago, etc. getting fuzzier as the delta increases. I've modified the code to give a relative date anywhere I saw an absolute date being used, but as I don't have Jira setup I'm currently unable to test this.

(using https://smartos.org/bugview/TOOLS-843 as an example)

before

Comment by Lloyd Dewolf
Created at 2015-03-06T18:26:30.000Z
Updated at 2015-03-06T18:28:30.000Z

after

Comment by Lloyd Dewolf
Created at 2015-03-06T18:26:30.000Z (5 days ago)
Updated at 2015-03-06T18:28:30.000Z (5 days ago)