Multi-file editor commit panel empty state

The commit panel should be opened automatically when the multi-file editor is opened to make sure new users instantly know where the commit button is. But it will be empty when it is first opened, and empty when ever a user commits all their changes.

We should make the empty state helpful and fun – perhaps like Slack when you're all caught up on unread messages.

Designs

When it is first opened	When all changed are committed	When staged is empty