Tracing: Untangle some includes

Forward declare in the header and include in the implementation where
possible.

Change-Id: Iea54f52fbf1deecab5f5a257821cd6383cf69a91
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/qmlprofiler/qmlprofilernotesmodel.cpp

@@ -25,6 +25,7 @@
 
 #include "qmlprofilernotesmodel.h"
 
+#include <tracing/timelinemodel.h>
 #include <utils/algorithm.h>
 
 namespace QmlProfiler {