add branch name validation to git VCS plugin

Task-number: QTCREATORBUG-8370

Change-Id: Iadca383dc01a55deab2cbfdb5ef439dfb0f2ab12
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/git/branchadddialog.h

@@ -55,6 +55,9 @@ public:
 
     bool track();
 
+private slots:
+    void updateButtonStatus();
+
 private:
     Ui::BranchAddDialog *m_ui;
 };