VCS: Introduce message style

Similar to compile and app output panes

Change-Id: Ib9ac6d8be880739ae78d0a39f7051cbe616e46c2
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/vcsbase/vcsbaseoutputwindow.h

@@ -106,6 +106,9 @@ public slots:
                        const QString &binary,
                        const QStringList &args);
 
+    // Append a blue message text and pop up.
+    void appendMessage(const QString &text);
+
 private:
     VcsBaseOutputWindow();