Keep track of authors across local commits and branch commits for suggestions

Previously, we would only show the authors based on local commits, but sometimes you want to set a commit author
to that of a commit on another branch. Now, so long as you've viewed the branch's commits, the author will appear
as a suggestion.

pkg/gui/controllers/switch_to_sub_commits_controller.go

@@ -70,6 +70,7 @@ func (self *SwitchToSubCommitsController) viewCommits() error {
 	}
 
 	self.setSubCommits(commits)
+	self.c.Helpers().Refresh.RefreshAuthors(commits)
 
 	subCommitsContext := self.c.Contexts().SubCommits
 	subCommitsContext.SetSelectedLineIdx(0)