Use timestamp with time zone for postgres sql

[anphung]

Without time zone:

• When creation_time is saved to db, it is save as local time e.g +0200 EET
• When creation_time is read from db, it is read as +0000 +0000
  E.g:

1. creation_time is initialized: 2014-03-26 17:05:30.889109334 +0200 EET
2. Save into db it becomes: 2014-03-26 17:05:30.889109
3. Read from db to creation_time, it becomes: 2014-03-26 17:05:30.889109 +0000 +0000

=> (1) != (3)

With time zone: (1) == (3)

Reference: lib/pq#247 (comment)

[cbusbey]

Whew, sorry this took so long to merge. Thanks! 🍻