Incoming Nationals President Stan Kasten has made it abundantly clear that his strategy for winning in Washington begins with rebuilding the team’s farm system, which is barely left intact after years of MLB ownership. On Monday night, the Nats laid a stone in the foundation, by signing 17-year-old slugger Chris Marrero of Miami. He played 3rd base in high school, but with Ryan Zimmerman projected there long-term in the big leagues, the team anticipates a…