Git: Introduce MergeTool support

Change-Id: I906c3c692d9f4819bdf2a1489c42ae04f292894d
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/git/gitsubmiteditor.h

@@ -56,6 +56,7 @@ public:
 
 signals:
     void diff(const QStringList &unstagedFiles, const QStringList &stagedFiles);
+    void merge(const QStringList &unmergedFiles);
 
 protected:
     QByteArray fileContents() const;