Automate company sponsorships

Currently, company sponsorships are done manually so we can request logos that work on our dark background. However, we don't get notified when a company cancels their sponsorship so we have to check back monthly and remove anyone that stops sponsoring.

It would be great to automate this process. Maybe the easiest step is to notify us when someone stops sponsoring.

The issue names no files, tests, sponsorship provider, or notification destination. Start by identifying how company sponsorships are currently recorded on the gulp website and what service can report cancellations; done should include a defined automated cancellation notification workflow and removal process.

Written by the indexing model from the issue text.