Optional ability to download multiple files

**As a** _researcher_,

**I want** _the option to download multiple import files_

**so that** _I can speed up the process of downloading multiple files_.

### Conditions of Satisfaction
- In the `Approved Exports` view, a mechanism to select all files initiates a batch download.
- In the `Approved Imports` view, a mechanism to select all files initiates a batch download.