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/viewer/viewerglwidget.h

@@ -30,6 +30,8 @@
 #include "render/color.h"
 #include "render/colormanager.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief The inner display/rendering widget of a Viewer class.
  *
@@ -262,4 +264,6 @@ private slots:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // VIEWERGLWIDGET_H