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/task/task.h

@@ -26,6 +26,8 @@
 
 #include "common/cancelableobject.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A base class for background tasks running in Olive.
  *
@@ -143,4 +145,6 @@ private:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // TASK_H