Bulk Upload Changes

## Current issues:

~~Spreadsheets uploaded are only deleted after request succeeds. On failure, they remain on disk~~
- [ ] Update / create documentation
- [x] Awarded based on unused "student ID"; change to email address
- [x] Transactions are ungrouped, with no way to undo all at once

## What:
Enable two scenarios:
### Scenario 1:

- [x] Apply a list of transactions ~~(positive or negative)~~

Ex:
| User | Amount |
|--------|--------|
| `swider@example.com` | 3 |
| `coustan@example.com` | 4 |
| `chan@example.com` | 5 |

### Scenario 2:

- [x] Send the same amount to a list of people (Ex: Wildkit Academy)

Ex:
| User |
|--------|
| `swider@example.com` |
| `coustan@example.com` |
| `chan@example.com` |