Git: Add push to branch view

Allows pushing the selected local branch to any remote branch.

Change-Id: I6fb9ee8e1659070c1c759fe64b713fb2235c8816
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/branchview.h

@@ -82,6 +82,7 @@ private:
     void rebase();
     bool cherryPick();
     void log(const QModelIndex &idx);
+    void push();
 
     QToolButton *m_addButton = nullptr;
     QToolButton *m_refreshButton = nullptr;