Electric car maker Tesla Motors plans to open its first store in the city of Boston to show off its vehicles — the third retail location in the Bay State for the California-based firm. It's not known exactly when the Tesla (Nasdaq: TSLA) store, located in Copley Place in Boston's Back Bay, will open. Take a look at a photo gallery showing the inside of a Tesla stores. "We are excited to have a larger presence in Boston," said a Tesla spokeswoman in an email, adding the store would host an…