Implement string based search & replace in multiple files.

This uses the same UI as "Rename Symbol".
Moves the actual rename implementation to a static method in
BaseFileFind and uses it for rename symbol and search & replace.
Moves the signal notification for the code model from VCSManager to
the more general FileManager.
Note that as for rename symbol, there's no undo yet.

Task-number: QTCREATORBUG-73

src/plugins/coreplugin/filemanager.cpp

@@ -781,6 +781,11 @@ void FileManager::setFileDialogLastVisitedDirectory(const QString &directory)
     d->m_lastVisitedDirectory = directory;
 }
 
+void FileManager::notifyFilesChangedInternally(const QStringList &files)
+{
+    emit filesChangedInternally(files);
+}
+
 // -------------- FileChangeBlocker
 
 FileChangeBlocker::FileChangeBlocker(const QString &fileName)