Add CLA reporting functionality

:fork_and_knife: Add CLA reporting functionality that will generate a CSV of signed CLAs every month and send it out to a specified configurable email address.
Is there a reason the `content_type` is just matching `text` here, instead of something more specific to CSV, like `text/csv` or even just `csv`?  If someone uploads `myfile.txt`, which would be detected as `text/plain`, I'm guessing that will pass this validation, no?