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/project/projectviewmodel.h

@@ -26,6 +26,8 @@
 #include "project.h"
 #include "undo/undocommand.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief An adapter that interprets the data in a Project into a Qt item model for usage in ViewModel Views.
  *
@@ -239,4 +241,6 @@ private:
   QVector<ColumnType> columns_;
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // VIEWMODEL_H