Charlie Greene, the cofounder and CEO of Remento, first learned about the importance of recording memories when his father, Don Greene, died during the hijacking of United Airlines Flight 93 on 9/11. A 10-year-old boy at the time of the terrorist attack, which resulted in his father’s plane crashing in Shanksville, Penn., the now 34-year-old Greene mostly has a collection of old home videos to remember him by. So when his mother Claudette, 74, …