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/common/qtutils.h

@@ -29,6 +29,10 @@
 
 #include <QFontMetrics>
 
+#include "common/define.h"
+
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief Retrieves the width of a string according to certain QFontMetrics
  *
@@ -37,4 +41,6 @@
  */
 int QFontMetricsWidth(QFontMetrics fm, const QString& s);
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // QTVERSIONABSTRACTION_H