Add timezone offset to due date

Due Dates are ambiguous. It should capture the time based on the user's profile timezone settings.

Currently, it stores without time value.

Compare vs. the Created Date on a server running on UTC time:

+---------------------+---------------------+
| created             | duedate             |
+---------------------+---------------------+
| 2013-05-03 21:21:35 | 2013-05-03 00:00:00 | 
+---------------------+---------------------+

This can lead to inconsistent rendering of the duedate, especially if the server is on UTC time, and users are scattered around the world.

Example:

On the issue view, it'll show me one date, but when using the jiraissues macro, it shows a date behind.