Introduce "DiffusionCommitGraphView", which unifies "HistoryListView" and "HistoryTableView"

Summary:
Ref T13552. Currently, commit lists are sometimes rendered as an object list and sometimes rendered as a table. There are two separate views for table rendering.

Add a fourth view ("list, with a graph") with the eventual intent of unifying all the other views. For now, this only replaces "HistoryListView" -- and needs some more work to really be a convincing replacement.

Test Plan:

• Looked at "History" in Diffusion, saw an ugly view with all the information we want.
• Grepped for "HistoryListView", no hits.

Maniphest Tasks: T13552

Differential Revision: https://secure.phabricator.com/D21410