Slack Email Invites

[apex-omontgomery]

Adding an issue so this doesn't get lost. This is the ruby gem BE uses to send invites to slack.

Uninstalling this application from the slack channel will require reinstalling it and replacing the
SLACK_TOKEN
SLACK_CLIENT_SECRET
SLACK_CLIENT_ID
https://api.slack.com/docs/working-with-workspace-tokens#

So that you can fix the invites.

This bit of knowledge was lost, and following a cleanup of installed apps, we lost the ability to send invites from BE.