fix departments and downloads in data download, closes #564

[fgregg]

Overview

Fixes bug from #564.

Test

• pull down fix_units_in_data_download branch
• visit a unit and a department
• download a CSV
• make sure that employees are listed as belonging to the right department

[fgregg]

Note that Cook County SD 130 still looks the same.

name	unit	department
Karina, Alatorre		Cook County SD 130

I think this is acceptable because on the unit page, employees are listed as belonging to the Cook County SD 130 department.