Git: Added ability to checkout and reset in GitEditor

Especially useful in reflog.

Change-Id: I1d63221f152ebc7e69934482785b433d016e4ead
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>

src/plugins/git/giteditor.h

@@ -55,6 +55,8 @@ public slots:
     void commandFinishedGotoLine(bool ok, int exitCode, const QVariant &v);
 
 private slots:
+    void checkoutChange();
+    void resetChange();
     void cherryPickChange();
     void revertChange();
     void stageDiffChunk();