High-powered veterans of Google, Uber, Rocket Fuel and Zynga have joined a startup that aims to help educators reinvent elementary school teaching for the 21st Century. Joining AltSchool CEO Max Ventilla in his quest are former Google Distinguished Engineer Bharat Mediratta, who has been appointed CTO; Michael Ginty, previously Uber Technologies' head of global security, who is head of safety; Sue Yoon, a former vice president of the ad tech firm Rocket Fuel,; and Rajiv Bhatia, former director of…