Implement student upload page

[karthikv]

Still a lot to do in this PR:

• [x] Create student upload page
• [x] Use Evangelist for PDF -> JPEG conversion
• [x] Secure requests to Evangelist with a custom SSL cert
• [x] Only show submit tab if homeworks exist
• [x] Add submission time
• [x] Let students map pages to question parts
• [x] Add small JPEGs back to Assessment model
• [x] Use affix for better scrolling
• [x] Address any other TODOs in the code
• [x] Turn off submissions after the deadline

Will ping when it's ready.

[karthikv]

@karanveerm @catherinelu Ready for review. Securing requests with a custom SSL cert is easiest once I spin up a server for evangelist.

[karthikv]

Fixed all these issues.