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/projectexplorer/projectexplorericonviewitemdelegate.h

@@ -23,6 +23,10 @@
 
 #include <QStyledItemDelegate>
 
+#include "common/define.h"
+
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief The delegate that's used to draw items when ProjectExplorer is in Icon view
  */
@@ -34,4 +38,6 @@ public:
   virtual void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override;
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // PROJECTEXPLORERICONVIEWITEMDELEGATE_H