Fix dom structure for action item modals

The `form-group` element for Time inputs was outside the `modal-body` elements for adding comments, reopening items, and marking items as in-progress. This was creating this style issue:
![screenshot from 2014-07-01 10 33 20](https://cloud.githubusercontent.com/assets/59292/3444765/3716b9d6-0131-11e4-9cdc-73a53cc1281b.png)

Where it should look like this:
![screenshot from 2014-07-01 10 35 38](https://cloud.githubusercontent.com/assets/59292/3444768/3a384b84-0131-11e4-8cf7-c33261751e89.png)