various: encapsulate all code in the olive namespace to avoid name collisions

Large-scale code cleanup. Also adds a license to the top of all files that were
missing it.

app/panel/viewer/viewer.cpp

@@ -20,6 +20,8 @@
 
 #include "viewer.h"
 
+OLIVE_NAMESPACE_ENTER
+
 ViewerPanel::ViewerPanel(QWidget *parent) :
   ViewerPanelBase(parent)
 {
@@ -39,3 +41,5 @@ void ViewerPanel::Retranslate()
 
   SetTitle(tr("Viewer"));
 }
+
+OLIVE_NAMESPACE_EXIT