The pch creation so far used signal and slots but there was no explicit
pipeline. This patch is introducing the same architecture like the
refactoring plugin. It is filtering out older project parts from the
pipeline.
Change-Id: Iaa6bd2ca1272231b97ebe1f5f7b2ce8e43bc590c
Task-number: QTCREATORBUG-21111
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
