Better format the Next and Updated columns in MetaMTA Mail Queue

Summary: They were only displaying seconds. I found a function in viewutils.php that allowed for single-unit precision formatting, but I wanted more, so I wrote another function to allow more detail.

Test Plan: [site]/mail, and watch it work. It's a new function, so it shouldn't break anything else.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Maniphest Tasks: T1296

Differential Revision: https://secure.phabricator.com/D2616