Fixing the default dates.

Added set_default_dates function to the eve_backend so that we don't have to set the _updated and _created while using services directly.
dates are comparable, so you can say `self.assertEqual(date1, date2)` or `self.assertGreaterEqual(date1, date2)` etc [assert methods](https://docs.python.org/2/library/unittest.html#assert-methods)