Clearer and more relevant Slack notifications

It's clear you all love Slack notifications for your deploys. However, we knew we could do better at making it immediately obvious what changed, when it happened and who was responsible.

Every notification now starts with a quickly identifiable emoji so you can understand what kind of event occurred and a deep link to Sleuth to find out more. Next we put the "what" of the change front and center. Finally, messages call out the author and any important attributes of the notification.