Add ability to specify time for a new task

Currently we can specify date, e.g.:

``` bash
./myTasks.py -n "Tasks list" "task3" 2013-09-06
```

It would be good to specify also time for a new task, e.g.:

``` bash
./myTasks.py -n "Tasks list" "task3" 2013-09-06 2013-09-06T10:11:12.000Z
```
