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/widget/menu/menu.h

@@ -24,6 +24,10 @@
 #include <QMenuBar>
 #include <QMenu>
 
+#include "common/define.h"
+
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A menu widget for context menus and menu bars
  *
@@ -171,4 +175,6 @@ private:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // WIDGETMENU_H