Migration announcement

Adds text to Slack room announcements when a deployment is being made with migrations. Also adds deployed branch and stage to completion announcement.

Command: `cap production deploy:migrations -s branch=master`

Previous text: `Joshua Puetz is deploying Core's master to production`
Previous completion text: `Joshua Puetz deployed Core successfully in 228 seconds`

New text: `Joshua Puetz is deploying Core's master with migrations to production`
New completion text: `Joshua Puetz deployed Core's master with migrations to production successfully in 228 seconds`