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/taskmanager.h

@@ -27,6 +27,8 @@
 #include "common/constructors.h"
 #include "task/task.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief An object that manages background Task objects, handling their start and end
  *
@@ -182,4 +184,6 @@ private slots:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // TASKMANAGER_H