properly align group headers to the right of the selection checkbox when...

... multiselect is enabled.

When multiselect was enabled previously, the group header would overwrite the selection checkbox and be crammed into the narrow checkbox column as it always used the first column of the row. It now checks to see if multi-select is enabled, and if so, it uses the second column instead.

---

__General Requirements__
- [ ] Pull Request contains full description of changes
- [ ] Link to the Pivotal Tracker story
- [ ] Rebased against latest master branch
- [ ] There are no `-1` code reviews (can only be overridden by Kyle)

---

__Coding Standards__
- [ ] Style guidelines are followed, code has been formatted
- [ ] Code follows idiomatic language paradigms

---

__UI/UX__
- [ ] applicable (UI/UX has been changed)
- [ ] reviewed for usability and design

---

__Defect__
- [ ] Feature or defect resolution has been manually tested and meets all requirements of the underlying story
- [ ] Root cause analysis provided