Patch Set 4:

Looks nice. I think the toggles for amend, changeid and signedOff and preferences should be part of the view menu.
In change http://egit.eclipse.org/r/#change,3503 I implemented committing from staging view. I also reuse the commit message part of CommitDialog, but the widgets are created outside the component. This provides the flexibility to have a different UI in Commit Dialog and Staging View.