Simplifies the use of MultiSourceWidget

Widgets that embed MultiSourceWidget no longer have to explicitly call
loadSources(). This is done as part of the set-up for MultiSourceWidget.

modules/mercurial/widget.go

@@ -45,7 +45,6 @@ func NewWidget(app *tview.Application, pages *tview.Pages, settings *Settings) *
 		settings: settings,
 	}
 
-	widget.LoadSources()
 	widget.SetDisplayFunction(widget.display)
 
 	widget.HelpfulWidget.SetView(widget.View)