upload bp cleanup

note: this won't be introducing any major features or anything, just refactoring and cleanup!

• created new package just for upload bp!
  • exif functions moved out of main bp for tidiness
  • virus scanning fns moved out of main bp as well
• the virus background task logic was also improved (asyncio.wait → asyncio.wait_for)
• unrelated: tox env was changed from py36 → py3