implemented speed/duration dialog and most of its functionality

An earlier commit implementing media in and out parameters was primarily for
this addition. A simple control dialog for the clip's speed presentation
reimplemented from the old codebase.

app/widget/timelinewidget/view/timelineview.cpp

@@ -46,6 +46,7 @@ TimelineView::TimelineView(const TrackType &type, Qt::Alignment vertical_alignme
   setDragMode(NoDrag);
   setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
   setBackgroundRole(QPalette::Window);
+  setContextMenuPolicy(Qt::CustomContextMenu);
 
   connect(&scene_, SIGNAL(changed(const QList<QRectF>&)), this, SLOT(UpdateSceneRect()));