(a) The code model manager figures out by itself which files were added
    or removed from the project.

    If this was done successfully, check also the timestamp of the
    common files and reindex if necessary.

(b) A full reindexing is only triggered if the project configuration
    changes (defines, includes, framework paths).

(c) If project files were removed, the garbage collector is called.

Task-number: QTCREATORBUG-9730
Change-Id: Ib855614b070880576233a3525813617c967a72f3
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>