Fix timezone issue

This fixes an issue where the timesheet history in the app would display inconsistent dates depending on the timezone.

Harvest saves each timesheet entry according to the user's timezone setting in Harvest. The issue was happening because Date.parse was trying to parse the date as UTC and then converting to local time. More info here: http://blog.dygraphs.com/2012/03/javascript-and-dates-what-mess.html

/cc @s-vizzari @jamesarosen @jakeisonline