Changes display of People page.

* Removes ordering by department, opting instead to display people in
  alphabetical order by their last name.
* Splits up listing between full-time staff and students. We'll need to
  add a category to People posts called "Student Assistant" to display
  them correctly.
* Uses flexbox to display them in the grid, which fails in IE9 and
  older. Need to add a good fallback for this.