VCS[git]: Add support for cleaning a repository.

Present user with a checkable list of files to be cleaned (add reusable
dialog to VCSBase module).

src/plugins/git/gitplugin.h

@@ -105,6 +105,7 @@ private slots:
     void undoRepositoryChanges();
     void stageFile();
     void unstageFile();
+    void cleanRepository();
 
     void showCommit();
     void startCommit();
@@ -146,6 +147,7 @@ private:
     QAction *m_commitAction;
     QAction *m_pullAction;
     QAction *m_pushAction;
+    QAction *m_cleanAction;
 
     QAction *m_submitCurrentAction;
     QAction *m_diffSelectedFilesAction;