Add limit for total file uploads

[catarak]

Each user should have a limit on the total size of the files they've uploaded to S3.

[uttpal]

@catarak I would like to fix this issue

[catarak]

awesome! it may make sense to work on #167 or #169 first, and #167 has an open PR, #222, with a bug so it hasn't been merged yet.

[dhruvdutt]

@catarak All the issues you pointed are closed now.
Can I work on this one now since it's in high priority?

[catarak]

definitely! i think this one will take a little bit of time. let me know if you get stuck!