Display noDataString for no commits in DiffusionCommitGraphView
Summary:
When a user has no commits, the view is empty. Instead display an explanation similar to the existing text for no revisions.
Closes T16200
Test Plan:
* Go to http://phorge.localhost/people/commits/1/ for a user who has no commits. See a placeholder text explanation instead of emptiness.
* Go to http://phorge.localhost/people/commits/2/ for a user who has commits. See a blue header "Recent Commits", similar to "Recent Revisions" shown regardless of existing revisions or not.
Reviewers: O1 Blessed Committers, valerio.bozzolan, mainframe98
Reviewed By: O1 Blessed Committers, valerio.bozzolan, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16200
Differential Revision: https://we.phorge.it/D26227