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/taskview/taskviewitem.h

@@ -28,6 +28,8 @@
 
 #include "task/task.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A widget that visually represents the status of a Task
  *
@@ -53,4 +55,6 @@ private:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // TASKVIEWITEM_H