implemented a footage viewer

Essentially a minor derivation of a viewer type that can automatically view
footage from the project (i.e. not in a sequence).

app/panel/viewer/viewerbase.cpp

@@ -0,0 +1,56 @@
+#include "viewerbase.h"
+
+ViewerPanelBase::ViewerPanelBase(QWidget *parent) :
+  PanelWidget(parent)
+{
+}
+
+void ViewerPanelBase::ZoomIn()
+{
+  viewer_->SetScale(viewer_->scale() * 2);
+}
+
+void ViewerPanelBase::ZoomOut()
+{
+  viewer_->SetScale(viewer_->scale() * 0.5);
+}
+
+void ViewerPanelBase::GoToStart()
+{
+  viewer_->GoToStart();
+}
+
+void ViewerPanelBase::PrevFrame()
+{
+  viewer_->PrevFrame();
+}
+
+void ViewerPanelBase::PlayPause()
+{
+  viewer_->TogglePlayPause();
+}
+
+void ViewerPanelBase::NextFrame()
+{
+  viewer_->NextFrame();
+}
+
+void ViewerPanelBase::GoToEnd()
+{
+  viewer_->GoToEnd();
+}
+
+void ViewerPanelBase::ShuttleLeft()
+{
+  viewer_->ShuttleLeft();
+}
+
+void ViewerPanelBase::ShuttleStop()
+{
+  viewer_->ShuttleStop();
+}
+
+void ViewerPanelBase::ShuttleRight()
+{
+  viewer_->ShuttleRight();
+}