QmlProfiler: Move parts of model manager and trace file to Timeline

This way we can use the trace file loading and saving mechanism for
other profilers.

Change-Id: I98ec1cdde6f7abcea152cabf72e64d4e696dfa59
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/qmlprofiler/tests/debugmessagesmodel_test.cpp

@@ -39,7 +39,7 @@ DebugMessagesModelTest::DebugMessagesModelTest(QObject *parent) :
 
 void DebugMessagesModelTest::initTestCase()
 {
-    manager.startAcquiring();
+    manager.initialize();
     QmlEvent event;
     event.setTypeIndex(-1);