Use phabricator_ time functions in more places

Summary:
Replace some more date() calls with locale-aware calls.

Also, at least on my system, the DateTimeZone / DateTime stuff didn't actually
work and always rendered in UTC. Fixed that.

Test Plan:
Viewed daemon console, differential revisions, files, and maniphest timestamps
in multiple timezones.

Reviewed By: toulouse
Reviewers: toulouse, fratrik, jungejason, aran, tuomaspelkonen
CC: aran, toulouse
Differential Revision: 530