Backfill UI almost done

[michaeldaou]

What I have right now:

• Standard+ users can change a loan from status "LENT" to status "BACKFILL_REQUESTED" by clicking the "request backfill" button, which opens a modal and allows you to upload a PDF. Once PDF is uploaded, user will submit the request, thus closing the modal and changing the status of the item.
• Manager+ users can approve and deny backfill requests and also view the associated PDF. (PDF viewing is contingent upon Henry fixing something on the backend.)
• If backfill request is approved, item becomes DISBURSED. If backfill request is denied, item becomes LENT again.

What's missing:

• Right now, user can make backfill request without uploading a receipt.
• Cannot upload a new PDF after the backfill request has been made
• Cannot leave comments, is this required?
• The GUI is still kinda shit

[michaeldaou]

Updated the PR descriptions, please reread.

[tomrom95]

Private comments are required in our variance