Social network Twitter‘s (NYSE: TWTR) top ranks shuffled around last week, emphasizing a time of change at the company. On Thursday, Twitter announced that it’s bringing onboard tech executive Keith Coleman as vice president of product, filling an important position that has been vacant since January. And on Friday, Richard Alfonsi, one of Twitter’s top ad-sales leaders, announced he was leaving the company and joining Stripe, an online payments company for start-ups in the United States.