Merge branch 'treeview'

Merge branch 'treeview'

* treeview:
  dag: Move TODO file to the 'todo' branch
  views.dag: Show more edges
  git-dag: Show more nodes by default and limit to local branches
  views.dag: Add arrows to graph edges
  views.dag: Add GitDAGWidget
  views.dag: Add horizontal wheel panning
  views.dag: Update _zoom when scaling
  views.dag: Mouse wheel pans, add control to zoom
  views.dag: Zoom more
  Added TODO list for treeview branch
  views.main: Add 'DAG...' to the tools menu
  models.main: Factor out history methods into models.commit
  git: Remove the test for None
  Remove 'remotes/' and 'heads/' from branch names in dag view
  Add sha1 and branch/tag text to the nodes (and give them some space)
  Make room for text in the node by providing each with an internal glyph
  Set background color the simple way with the background brush
  Add additional interesting info to Commits
  treeview: add a graphical history viewer
  models: add a commits() method for traversing history