Bug/grouped column reorder

Allow grouped headers to reflect any changes in column re-ordering.

Pivotal Story: 51573875 (Data Grid widget shows wrong header for data.)


__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

---

__Testing__
- [ ] Test coverage has not decreased
- [ ] There is no performance degradation
- [ ] All appropriate automated tests are present
- [ ] Appropriate seed data exists


---

__Documentation__
- [ ] Major design decisions have been documented on the wiki
- [ ] Deployment impact (changes required for new services, configuration, etc.)
- [ ] documentation links from Pull Request

---

__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
- [ ] Seed data sufficient to satisfy testing resolution of defect
- [ ] Root cause analysis provided